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ELEMENTARY  ELECTRO-TECHNICAL  SERIES 


ELECTRIC  HEATING 


BY 

EDWIN  J.  HOUSTON,  Ph.  D.,  (Princeton) 

AND 
A.  E.  KENNELLY,  Sc.  D. 


NEW  YORK 

THE  W.  J.  JOHNSTON  COMPANY. 

253  Broadway 

1895 


COPYRIGHT,  1895,  BY 
THE  W.  J.  JOHNSTON  COMPANY. 


PREFACE 

IN  preparing  this  volume  on  ELECTRIC 
HEATING,  as  one  of  a  series  entitled 
The  Elementary  Electro -Technical  Series, 
the  authors  believe  they  are  meeting  a 
demand,  that  exists  on  the  part  of  the  gen- 
eral public,  for  reliable  information  re- 
specting such  matters  in  electricity  as 
can  be  readily  understood  by  those  not 
especially  trained  in  electro -technics. 

The  subject  of  electric  heating  is  to- 
day attracting  no  little  attention.  The 
wonderful  growth  in  electric  street  rail- 
ways, coupled  with  the  readiness  with 
which  the  current  can  be  applied  to 
the  heating  of  the  cars,  together  with 
the  marked  efficiency  of  the  electric  air 
heater  as  an  apparatus  for  transforming 
electric  energy  into  heat  energy,  have, 
during  the  last  decade,  caused  a.  develop- 


M289309 


IV  PKEFACE 

ment  in  electric  car  heating.  But  the 
growth  of  electric  heating  has  by  no 
means  been  limited  to  this  particular 
field.  The  development  of  electric  cook- 
ing apparatus  has  naturally  attended  the 
extensive  distribution  of  electricity  for 
lighting  and  power,  and  electric  cooking 
is  now  taking  its  place  with  electric  light- 
ing as  an  adjunct  to  the  modern  house. 

In  the  direction  of  the  employment  of 
powerful  electric  currents  for  heating 
effects,  process-es  for  electric  welding,  and 
the  electrical  shaping  and  forging  of  met- 
als, are  coming  into  commercial  use,  and 
applications  are  daily  being  made  of  the 
power  of  electricity  in  electric  furnaces, 
either  where  the  heating  effect  alone  is 
employed,  or  where  both  heating  and 
electrolytic  effects  are  utilized. 


CONTENTS 

PAGE 

I.     INTRODUCTORY 7 

II.     ELEMENTARY  PRINCIPLES  .     .  30 

III.  ELECTRICAL  HEATING  OF  BARE 

CONDUCTORS 37 

IV.  ELECTRICAL  HEATING  OF  COV- 

ERED CONDUCTORS    ...  69 

V.     FUSE  WIRES 87 

VI.     ELECTRIC  HEATERS  .     .     .     .  117 

VII.     ELECTRIC  COOKING      .     .     .  151 

VIII.     ELECTRIC  WELDING      ...  181 

IX.     ELECTRIC  FURNACES     .     .     .  233 

X.     MISCELLANEOUS  APPLICATIONS 

OF  ELECTRIC  HEATING  .     .  255 

INDEX  271 


ELECTRIC  HEATING. 


CHAPTER  I. 

INTRODUCTORY. 


ZOROASTER,  the  founder  of  fire  worship, 
because  of  the  many  advantages  mankind 
derived  from  fire,  bade  his  followers  wor- 
ship the  sun  as  its  prime  and  sustaining 
cause.  Although  the  idolatrous  doctrine 
of  the  old  Persian  is  now  entirely  dis- 
credited by  civilized  races,  yet  the  truth 
of  the  belief  that  found  in  the  sun  the 
source  of  all  the  thermal  phenomena  of 
the  earth,  still  remains  unchallenged.  It 


5  ELECTRIC   HEATING. 

can  be  shown,  from  a  scientific  point 
of  view,  that  in  reality,  there  is  not  one 
of  the  many  ways  in  which  man  can 
produce  heat  on  the  earth,  that  cannot 
trace  its  prime  cause  to  the  sun. 

Take,  for  example,  one  of  the  common- 
est methods  of  obtaining  heat;  namely, 
by  the  burning  of  a  mass  of  coal.  Here  it 
is,  at  first  sight,  by  no  means  evident,  that 
the  heat  of  the  glowing  mass  was  derived 
from  the  sun.  In  accordance  with  mod- 
ern scientific  belief,  heat  is  no  longer  re- 
garded as  a  kind  of  matter,  but  as  a  con- 
dition of  matter.  A  hot  body  differs 
from  a  cold  body  in  that  the  very  small 
particles  or  molecules,  of  which  it  is  com- 
posed, are  in  a  state  of  rapid  to -and- fro 
motions  or  oscillations.  When  a  hot 
body  grows  hotter,  the  only  effect  pro- 
duced, unless  the  body  is  melted  or  evap- 


INTEODUCTORY.  9 

orated,  is  to  increase  the  violence  of  these 
molecular  oscillations.  Could  we  de- 
prive a  body  of  all  its  heat  its  oscillations 
would  entirely  cease.  In  order  to  pro- 
duce molecular  or  heat  oscillations,  en- 
ergy must  be  expended  on  the  body ;  that 
is,  work  must  be  done  on  its  molecules. 
In  other  words,  a  hot  body  is  a  mass  of 
matter  plus  a  certain  quantity  of  molec- 
ular energy.  When  a  hot  body  cools,  it 
throws  off  or  dissipates  a  certain  quantity 
of  its  molecular  energy,  and,  when  the 
heat  thus  thrown  off  is  absorbed  or  taken 
in  by  another  body,  the  latter  thereby 
acquires  an  additional  store  of  energy. 
When  a  pound  of  coal  is  burnt  in  air,  the 
heat  produced  results  from  the  mutual 
attractions  existing  between  the  mole- 
cules of  the  carbon  and  the  molecules  of 
the  oxygen  in  the  air;  or,  from  what  is 
ordinarily  called  their  chemical  affinity. 


10  ELECTRIC  HEATING. 

Unburnt  coal  and  air  possess,  jointly,  a 
store  of  chemical  energy,  having  the 
power  or  potency  of  doing  work,  but 
actually  doing  no  work ;  while  coal  and  air 
after  burning,  no  longer  possess  this  store 
of  chemical  energy,  but  have  acquired  in 
its  place  a  stock  of  oscillation  or  heat  en- 
ergy; i.  e.,  energy  of  oscillation. 

Could  the  burning  be  effected  in  a  heat- 
tight  space,  this  oscillation  or  heat  energy 
would  be  entirely  confined  to  the  interior 
of  the  chamber,  but  as  no  bodies  are  per- 
fect non-conductors  of  heat,  such  a  heat- 
tight  space  cannot  be  obtained,  and  some, 
at  least,  of  the  oscillation  energy  will  be 
communicated  to  surrounding  bodies. 

A  steam  engine  is  a  machine  for  pro- 
ducing mechanical  energy  at  the  expense 
of  molecular  oscillation  energy.  If  we 
suppose  that  a  pound  of  coal  could  be 


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s 

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burned  in  connection^with ja_  theoretically 
perfect  steam  engine,  with  the  necessary 
quantity  of  air,  all  the  molecular  oscilla- 
tion energy  developed  by  the  combustion 
could  be  utilized  by  the  engine,  which 
would  do  an  amount  of  work  exactly 
equal  to  the  amount  of  original  chemical 
energy  residing  in  the  coal  and  air.  It  is 
known,  as  the  result  of  calculation,  that 
such  an  engine  would  be  capable  of  doing 
an  amount  of  work  represented  by  the 
lifting  of  one  pound  through  a  height  of 
about  2000  miles.  When,  therefore,  a 
pound  of  coal  is  burnt  with  air,  an  amount 
of  oscillation  energy  is  developed,  equal 
to  that  which  would  be  obtained  by  the 
falling  of  that  pound  of  coal  from  a  height 
of  about  2000  miles.  Owing  to  a  variety 
of  circumstances,  however,  the  best  steam 
engines  are  only  capable  of  yielding  about 
15  per  cent,  of  this  work. 


12  ELECTEIC  HEATING. 

The  store  of  energy  existing  in  a  pound 
of  coal  was  obtained  from  the  sun's  radia- 
tion during  the  geological  past.  That  is 
to  say,  during  the  Carboniferous  Age,  the 
carbon  of  the  coal  originally  existed  in 
the  earth's  atmosphere  combined  with 
oxygen  as  gaseous  carbon  dioxide.  For 
the  formation  of  every  pound  of  coal  ex- 
isting in  the  earth's  crust  a  definite 
quantity  of  carbonic  acid  gas  was  dissoci- 
ated, or  separated  into  carbon  and  oxy- 
gen, by  means  of  the  energy  of  the  sun's 
rays  absorbed  by  the  vegetation  of  the 
Carboniferous  Era.  In  other  words,  the 
leaves  of  the  carboniferous  flora  absorbed 
gaseous  carbon  dioxide  from  the  atmos- 
phere, and,  in  the  delicate  laboratories  of 
the  leaf,  by  means  of  the  energy  absorbed 
directly  from  the  sun's  rays,  a  dissocia- 
tion occurred  between  the  carbon  and  the 
oxygen.  The  ability,  therefore,  of  the 


INTKODUCTOKY.  13 

carbon  to  again  recombine  with  oxygen  in 
the  form  of  gaseous  carbon  dioxide  has 
been  a  result  of  energy  expended  on  the 
plant  and  lodged  in  the  carbon  of  its 
woody  fibre.  A  lump  of  coal,  therefore, 
is  in  reality  a  store- house  of  the  solar  heat 
of  an  early  geological  era. 

Viewed  in  this  light,  a  lump  of  coal  can 
be  regarded  as  not  unlike  a  weight  raised, 
say  from  the  ground  through  a  certain 
height.  Suppose,  for  example,  a  pound 
weight  be  attached  to  a  string  passing  over 
a  pulley  and  raised  to  a  height  of  20  feet 
from  the  ground,  and  that,  while  in  this 
position,  the  string  of  the  pulley  be  fixed. 
Evidently,  work  has  been  expended  in 
raising  the  pound  weight,  and,  as  a  result 
of  this  work,  the  weight  is  placed  in  a 
position  in  which  it  can,  at  any  time  the 
string  is  released,  fall  back  again  to  the 
ground,  and  in  so  doing  restore  the 


14  ELECTRIC  HEATING, 

amount  of  work  originally  expended  in 
lifting  it.  In  the  same  way,  a  pound  of 
coal  has,  by  the  work  of  the  sun,  been 
placed  in  a  condition  in  which  it  can 
combine  with  the  oxygen  of  the  air,  and 
burn.  In  so  doing  it  must  give  out  an 
amount  of  heat  equal  to  that  representing 
the  sun's  work  upon  it,  amounting,  as 
we  have  seen,  measured  in  units  of  the 
earth's  gravitational  work,  to  an  elevation 
of  about  2000  miles. 

But  it  was  not  only  during  the  geo- 
logical past  that  the  solar  energy  was 
thus  husbanded  in  the  earth's  crust. 
The  sun's  energy  is  to-day  being  similarly 
stored  in  all  vegetable  foods,  and  it  is 
on  this  store  that  animals  draw  for  their 
muscular  and  nervous  energy.  That  is  to 
say,  all  vegetable  products  represent 
chemical  stores  of  solar  energy.  An 
animal  is  capable  of  releasing  this  energy 


INTRODUCTORY.  15 

in  its  muscles  by  the  actual  combustion 
of  these  chemical  substances,  after  their 
proper  assimilation  in  its  body.  Muscu- 
lar activity,  therefore,  is  but  another  in- 
stance of  energy  primarily  obtained  from 
the  sun's  radiation.  The  earth's  animals 
are,  therefore,  in  this  sense  truly  children 
of  the  sun,  since  they  thus  indirectly  de- 
rive their  activity  from  that  luminary. 

Not  only  can  the  heat  and  consequent 
mechanical  motion,  which  it  is  possible  to 
obtain  by  the  burning  of  a  mass  of  coal, 
or  by  the  assimilation  and  consequent 
oxidation  of  a  certain  quantity  of  food  by 
an  animal,  be  traced  indirectly  to  the  sun, 
but  the  same  can  also  be  shown  to  be  true 
for  all  the  other  sources  of  mechanical  en- 
ergy with  which  we  are  acquainted  on  the 
earth.  Take,  for  example,  the  energy  de- 
livered to  a  windmill  from  moving  air,  or 


16  ELECTBIC   HEATING. 

to  a  water-wheel  from  flowing  water.  In 
the  case  of  a  windmill,  the  sun's  heat, 
acting  upon  the  air,  sets  up  convection 
currents,  or  winds,  whereby  the  work  ex- 
pended by  the  sun  in  heating  the  air  is 
liberated  in  mass  motion.  In  the  case  of 
a  water-wheel,  where  a  stream  of  water 
flowing  from  a  higher  to  a  lower  level  is 
caused  to  impart  its  energy  to  the  wheel, 
the  water,  in  reality,  occupies  a  position 
corresponding  to  a  raised  weight,  and  is 
able  to  do  work  because,  like  the  water,  it 
is  at  the  higher  level.  To  what  source  of 
energy  does  it  owe  this  ability  to  do  work? 
Manifestly  to  the  heat  of  the  sun,  where- 
by the  water  was  raised  as  vapor  and  sub- 
sequently fell  as  rain  on  the  slopes  of  the 
higher  level  from  which  it  is  now  flowing 
to  a  lower  level. 

The  molecules  of  a  hot  body  are  moving 


-Y  re 

/  )      ^  I 


to-and-fro  at  varying  veKHSftfes.  p  .  Some  are  v> 
moving  faster  than  others  ;  for^tiurmg  t&eir  ^ 
to-and-fro  motions,  they  frequently  col- 
lide, some  molecules  being  thereby  accel- 
erated and  others  retarded.  The  average 
molecule,  of  a  given  mass  possessing  a 
given  amount  of  heat,  may,  however,  be 
assumed  to  possess  on  the  whole,  a  cer- 
tain average  velocity  of  motion.  It  is 
clear,  therefore,  that  if  we  could  trans- 
form the  molecular  oscillations  of  a  heated 
body  into  a  motion  of  the  whole  mass,  the 
body  would  move  with  a  uniform  velocity 
which  would  be  its  average  molecular  ve- 
locity, in  the  sense  just  described.  This 
conception  is  valuable  as  affording  a  meas- 
ure of  the  amount  of  heat  possessed  by  a 
body.  Similarly,  when  work  is  done  upon 
a  body,  whereby  it  acquires,  or  is  capable 
of  acquiring,  a  certain  velocity  of  motion, 
this  motion  can  be  represented  by  an  agi- 


18  ELECTRIC  HEATING. 

tation  of  the  molecules  in  the  quiescent 
mass  of  the  body,  the  average  molecular 
velocity  corresponding  to  the  velocity  of 
the  mass.  Clearly,  therefore,  heat  repre- 
sents mechanical  work,  and  mechanical 
work  represents  heat.  Or,  in  other  words, 
a  certain  quantity  of  mechanical  work  is 
capable  of  being  expressed  as  a  definite 
quantity  of  heat,  or  a  certain  amount  of 
heat  is  capable  of  being  expressed  as  a 
definite  quantity  of  mechanical  work, 
even  though,  in  all  cases,  we  may  not, 
at  present,  possess  the  means  whereby 
the  actual  conversion  of  one  into  the  other 
can  be  effected. 

For  this  reason  a  given  quantity  of  heat 
can  only  be  made  to  produce  a  certain 
quantity  of  mechanical  work  correspond- 
ing thereto,  even  though  the  means  of 
conversion  were  so  perfect  that  no  loss 
should  take  place  during  the  process.  And 


INTRODUCTORY.  19 

similarly,  a  given  quantity  of  work  can 
only  be  capable  of  developing  a  fixed  quan- 
tity of  heat,  no  matter  how  perfect  the 
mechanism  of  conversion  may  be. 

Heat  developed  by  electricity  forms  no 
exception  to  the  preceding  principles. 
As  we  shall  see,  a  given  quantity  of  elec- 
trical energy  is  capable  of  producing  a 
fixed  quantity  of  heat,  no  matter  how 
such  heat  is  developed.  The  limit  to  im- 
provement in  electrical  heating  apparatus, 
as  in  any  other  machinery,  being  such 
as  will  insure  the  least  loss  of  energy 
during  the  process  of  conversion.  As  a 
matter  of  fact,  electrical  energy  can 
always  be  completely  converted  into 
heat,  although,  unfortunately,  the  con- 
verse is  not,  at  present,  true,  and  heat 
energy  cannot,  therefore,  be  completely 
converted  into  electrical  energy,  but 


20  ELECTRIC   HEATING. 

only  a  comparatively  small  fraction  can 
be  so  converted. 

It  is  a  fundamental  doctrine  of  modern 
science  that  energy  is  never  annihilated. 
It  apparently  disappears  in  one  form,  only 
to  reappear  in  another  form.  Thus,  heat 
energy,  or  molecular  motion,  when  disap- 
pearing as  such,  reappears  in  some  other 
form;  say,  for  example,  as  mass  motion, 
or  mechanical  energy.  Mechanical  energy 
may  in  its  turn  disappear  as  such,  to  pro- 
duce chemical,  thermal,  electromagnetic, 
or  some  other  form  of  energy.  In  all 
cases,  definite  quantitative  relations  exist 
between  the  amounts  of  energy  ex- 
changed, but  in  every  process  of  conver- 
sion a  tendency  exists  whereby  some  of 
the  energy  assumes  the  form  of  molecu- 
lar motion  or  heat,  in  which  it  is  often 
impossible  to  again  utilize  or  further 
transform  it. 


CHAPTER  II. 

ELEMENTAKY  PRINCIPLES. 

DURING  the  building  of  a  brick  wall,  a 
certain  amount  of  work  is  done  in  raising 
the  bricks  from  their  position  on  the 
ground  to  their  position  in  the  wall.  The 
amount  of  this  work  is  definite,  and  is 
measured  by  the  amount  of  force  re- 
quired to  raise  the  bricks  directly  against 
the  gravitational  pull  of  the  earth,  multi- 
plied by  the  vertical  distance  through 
which  they  are  raised. 

Care  must  be  taken  not  to  confuse  the 
ideas  of  force  and  work.  Force  may  be 
defined,  in  general,  to  be  that  which 
causes  a  body  to  move,  or  to  tend  tc 
move.  Work  is  never  done  by  a  force  uu- 


22  ELECTKIC   HEATING. 

less  it  actually  produces  a  motion  in  the 
body  on  which  it  is  acting.  For  example, 
when  a  brick  rests  on  a  wall,  or  on  the 
ground,  it  is  exerting  a  force  vertically 
downward  in  virtue  of  the  earth's  gravita- 
tional pull;  that  is  to  say,  it  is  pressing 
downward  against  the  earth,  with  a  force 
equal  to  its  weight,  approximately  six 
pounds'  weight,  but  this  force  is  not  doing 
work  since  it  is  not  producing  a  motion  of 
the  brick.  Work  had  to  be  done  on  the 
brick  when  it  was  raised  from  the  ground 
to  its  position  on  the  wall;  that  is,  a  mus- 
cular force,  equal  to  that  of  six  pounds' 
weight,  had  to  be  exerted,  in  order  to  over- 
come the  earth's  gravitational  attraction 
on  the  brick  and  this  force  had  to  be  con- 
tinuously exerted  while  the  brick  was 
being  raised  through  the  vertical  distance 
existing  between  the  ground  and  its  posi- 
tion in  the  wall.  Moreover,  if  the  brick 


ELEMENTARY  PRINCIPLES.  23 

be  permitted  to  fall  from  the  wall  to  the 
ground,  work  will  be  done  by  the  brick  in 
falling,  which  could  be  usefully  employed, 
as,  for  example,  in  winding  a  clock,  and 
the  amount  of  this  work  could  be  repre- 
sented, as  before,  by  the  weight  of  the 
brick  multiplied  by  the  distance  through 
which  it  falls.  This  amount  of  work 
must  be  equal  to  that  which  was  expended 
in  lifting  the  brick. 

In  order  to  measure  accurately  the 
amount  of  mechanical  work  done  on  a 
body  in  raising  it  through  a  given  vertical 
distance,  or  the  amount  of  work  done  by  a 
body  in  falling,  reference  is  had  to  certain 
units  of  work.  A  convenient  unit  of 
work,  much  employed  in  engineering,  in 
the  United  States  and  in  England,  is  called 
the  foot-pound,  and  is  equal  to  the  work 
done  when  a  force  equal  to  a  pound's 


24  ELECTRIC  HEATING. 

weight  acts  through  a  distance  of  one  foot. 

Suppose  a  uniform  brick  wall  con- 
taining 1000  bricks,  each  weighing,  say  six 
pounds,  has  its  top  six  feet  from  the 
ground.  The  total  weight  of  the  wall 
would  be  6000  pounds,  and  the  average 
distance  through  which  the  bricks  would 
have  to  be  raised,  in  building  the  wall, 
would  be  three  feet,  so  that  the  amount 
of  work  necessarily  expended  in  the  build- 
ing of  the  wall,  would  be  that  required 
to  raise  its  weight  through  its  average 
height,  or  6000  x  3  -  18,000  foot-pounds. 

The  foot-pound  is  not  employed  as  a 
unit  of  work  in  countries  outside  of  the 
United  States  and  Great  Britain,  nor  gen- 
erally in  scientific  writings  anywhere.  A 
unit  frequently  employed  is  called  the 
joule,  and  is  commonly  used  as  the  unit 


ELEMENTARY  PRINCIPLES.  25 

of  work  performed  by  an  electric  current; 
for,  as  we  shall  see,  electric  currents  are 
capable  of  doing  work.  The  value  of  the 
joule  may,  however,  be  conveniently  ex- 
pressed as  being  approximately  equal  to 
0.738  foot-pound;  or  to  the  work  done  in 
raising  a  pound  through  nearly  nine 
inches.  Thus,  the  amount  of  work  ex- 
pended in  the  building  of  the  brick  wall 
just  referred  to,  was  18,000  foot-pounds, 
or  approximately  24,000  joules. 

The  brick  wall  referred  to  in  the  pre- 
ceding paragraph  might  be  erected  by 
the  workmen  in  a  day,  or  in  six  days,  but, 
when  built,  the  amount  of  work  done 
would  be  the  same;  namely,  24,400  joules. 
Regarding  its  erection  from  the  standpoint 
of  each  workman,  the  rate  at  which  each 
man  would  have  to  expend  his  energy  in 
doing  the  work  would  be  very  different  in 


26  ELECTEIC  HEATING. 

the  two  cases,  since,  if  he  does  in  one 
day  that  which  he  would  otherwise  do  in 
six  days,  he  would  clearly  expend  his  en- 
ergy at  an  average  rate  six  times  greater 
in  the  former  case.  The  rate  at  which 
work  is  done  is  called  activity,  so  that  the 
average  activity  of  the  workman  would  be 
six  times  greater,  if  the  wall  is  built  in  one 
day,  than  if  it  be  built  in  six  days. 

A  unit  of  activity  is  the  foot-pound- 
per- second.  As.  generally  employed  in 
England  and  America,  the  practical  unit 
of  activity  is  the  average  activity  of  a  cer- 
tain horse  assumed  as  a  standard.  This 
unit  of  activity  is  called  the  horse-power, 
and  is  an  activity  of  550  foot-pounds-per- 
second.  The  unit  of  electrical  activity 
generally  used  all  over  the  world  and 
which  may,  therefore,  be  called  the  inter- 
national unit  of  activity  is  the  joule -per - 
second,  or  the  watt,  and  is  equal  to  0.738 


ELEMENTAKY  PRINCIPLES.  27 

foot-pound-per-second,  or  l-746th  of  a 
horse-power,  so  that  746  watts  are  equal 
to  one  horse-power. 

The  engines  of  an  Atlantic  liner  may 
develop  steadily  about  30,000  H.  P.  in 
driving  its  propeller.  This  represents  an 
activity  of  30,000  x  550  =  10,500,000 
foot-pounds,  or  8250  short-tons,  lifted  one 
foot-per-second,  or  one  short  ton  lifted 
8250  feet-per- second;  or,  expressed  in 
watts,  or  joules-per-second,  22,374,000. 

A  laborer  digging  a  trench  will  usually 
average  an  activity  of  only  50  watts,  or  36.9 
foot-pounds-per-second,  daring  his  work, 
so  that  the  average  activity  of  a  labor- 
ing man  may  be  taken  as  about  l-15th  of 
a  horse -power.  A  man  frequently  works, 
however,  at  an  activity  much  greater  than 
this,  say  at  an  activity  of  100  watts,  or 
about  l-8th  horse-power,  while  for  short 
periods,  say  for  half  a  minute,  he  can  sus- 


28  ELECTKIC  HEATING. 

tain  an  activity  of,  perhaps,  500  watts,  or 
even  746  watts,  or  one  horse -power. 

As  we  have  already  seen,  a  definite  and 
fixed  relation  is  maintained  between  the 
amount  of  heat  or  oscillation  energy 
present  in  a  unit  quantity  of  matter,  say 
a  pound  of  water,  and  the  amount  of  en- 
ergy which  must  be  expended  on  this 
matter  in  order  to  heat  it  to  a  given  tem- 
perature. The  amount  of  heat  energy  in 
an  indefinite  quantity  of  a  body,  such  as 
water,  cannot  be  determined  from  its 
temperature  alone;  we  require,  beside 
this,  to  know  its  mass.  If  we  know  its 
weight  in  pounds,  and  its  temperature  in 
degrees;  i.e.,  the  pound-degrees,  we  can 
determine  the  quantity  of  heat  energy 
existing  in  the  mass.  In  other  words, 
the  pound- degree  may  be  taken  as  a  heat 
unit,  and,  since  this  represents  a  definite 


PRCFCRTY 

ELEMENTARY  PRjfcir&LES.  29 


amount  of  work,  this  heat  unit-may 
its  value  expressed  either  in  joules  or  in 
foot-pounds.  The  British  heat  unit,  some- 
times called  the  British  thermal  unit,  or 
the  B.  T.  U.,  is  the  amount  of  heat  re- 
quired to  raise  a  pound  of  water  one  de- 
gree Fahrenheit,  from  59°  to  60°  F.  and  is 
taken  as  778  foot-pounds,  or  1055  joules. 
The  heat  unit  most  frequently  employed 
in  countries  other  than  the  United  States 
and  Great  Britain,  is  the  amount  of  heat 
required  to  raise  one  gramme  of  water 
lc  C.  This  heat  is  called  the  water- 
gramme-degree-centigrade,  the  lesser  ca- 
lorie, or  the  therm.  Expressed  in  foot- 
pounds, one  lesser  calorie  is  equal  to  4.18 
joules,  or  3.087  foot-pounds. 

The  amount  of  work  expended  in  heat- 
ing a  cubic  foot  of  water,  of  approximate- 
ly 62 2  pounds  weight,  from  50°  F.  to  the 
boiling  point  of  2123  F.,  or  through  a  tern- 


30  ELECTRIC  HEATING. 

peratureof  162°  F.,  is  approximately  62|  x 
162  =  1013  B.  T.  U.  ==  1,069,000  joules. 

A  reservoir  filled  with  water  possesses 
a  certain  store  of  energy,  or  capacity  for 
doing  work,  dependent  both  on  the 
amount  of  water  it  contains  and  on  the 
distance  through  which  the  water  is  per- 
mitted to  flow  in  escaping  from  the  reser- 
voir. In  accordance  with  what  has  al- 
ready been  stated,  the  amount  of  this 
work  can  be  represented  by  the  weight  of 
the  water  in  pounds,  multiplied  by  the 
distance  in  feet  through  which  the  water 
falls.  Thus,  consider  a  reservoir  holding, 
say  100,000  cubic  feet  of  water,  at  a  mean 
elevation  of  10  feet  above  a  pump  which 
fills  it.  The  weight  of  the  water  would 
be  approximately  6,250,000  pounds,  and 
the  amount  of  work  required  to  be  ex- 
pended by  the  pump  in  lifting  it  10  feet 


ELEMENTARY  PRINCIPLES.       31 

would  be  approximately  62,500,000  foot- 
pounds, or  84, 750, 000  joules.  If,  now,  this 
water  be  permitted  to  escape  to  the  pump 
level,  in  so  doing  it  will  expend  just  this 
amount  of  work.  If  the  distance  through 
which  the  water  fell  were  twice  as  great; 
i.e.,  if  the  pump  level  were  10  feet  lower 
down,  then  half  the  quantity  falling 
through  this  double  distance  would  do  the 
same  amount  of  work,  and,  of  course,  to 
fill  the  reservoir  through  such  a  distance 
would  necessitate  the  expenditure  of  twice 
as  much  work  as  in  the  former  case. 

Although  electricity  is  not  to  be  con- 
sidered as  a  liquid,  yet  many  of  the  laws 
which  relate  to  its  flow  are  similar  to  the 
laws  controlling  liquid  flow.  For  exam- 
ple, in  order  to  obtain  a  flow  of  water,  a 
difference  of  pressure  must  exist,  gener- 
ally in  the  form  of  a  difference  of  water 


32  ELECTEIC  HEATING. 

level,  and  the  direction  of  the  current  of 
water  is  from  the  higher  to  the  lower  pres- 
sure, or  from  the  higher  to  the  lower  level. 
So,  too,  in  order  to  obtain  a  flow  of  elec- 
tricity, a  difference  of  electrical  pressure 
or  level  must  exist,  or,  as  it  is  commonly 
called,  an  electromotive  force,  and  the  di- 
rection of  the  electric  current  is  assumed 
to  be  from  the  higher  to  the  lower  pres- 
sure, or  from  the  higher  to  the  lower  elec- 
tric level.  Just  as  in  the  case  of  the 
water  flow,  the  quantity  of  water  is  repre- 
sented by  some  unit  quantity,  such  as  a 
pound,  so  in  the  case  of  the  electric  cur- 
rent, the  quantity  of  electricity  is  repre- 
sented by  a  unit  of  electric  quantity  called 
a  coulomb;  and,  as  in  the  case  of  the  water, 
the  difference  of  level  is  represented  by 
some  such  unit  as  a  foot,  so  in  the  case  of 
the  electric  flow,  the  difference  of  electric 
pressure  or  level,  is  represented  by  a  unit 


ELEMENTARY  PRINCIPLES.  33 

called  the  volt.  Moreover,  as  the  amount 
of  work  done  by  a  given  quantity  of  wa- 
ter in  flowing,  is  equal  to  the  quantity  of 
water  represented,  say,  in  pounds,  multi- 
plied by  the  distance  through  which  it 
moves  in  feet,  the  work  being  expressed 
in  foot-pounds,  so  the  amount  of  work 
done  in  an  electric  circuit,  by  the  electric 
current  in  flowing,  is  equal  to  the  quanti- 
ty of  electricity  in  coulombs,  multiplied 
by  the  pressure,  or  the  difference  of  elec- 
tric level  through  which  it  flows,  in  volts. 
The  work  being  expressed  in  coulomb- 
volts,  or  joules,  a  joule  being  equal  to  one 
coulomb-volt.  In  point  of  fact  the  name 
joule,  for  a  unit  of  work,  was  first  em- 
ployed as  the  name  of  the  coulomb-volt, 
the  unit  of  electric  work. 

When  a  flow  of  100  coulombs  of  electric- 
ity passes  through  a  circuit  under  a  pres- 


34  ELECTRIC  HEATING. 

sure  of  50  volts,  the  amount  of  work  ex- 
pended by  the  electric  current  will  be  100 
x  50  =  5000  joules  =  3690  foot-pounds; 
one  coulomb  of  electricity  passing  under 
a  pressure,  or  through  a  difference  of  elec- 
tric level,  of  100  volts,  will  expend  the 
same  amount  of  work;  i.  e.,  100  joules,  as 
100  coulombs  passing  under  a  pressure  of 
one  volt.  An  electric  source,  such  as  a 
dynamo,  or  a  voltaic  battery,  is  a  device 
for  producing  an  electromotive  force;  that 
is,  a  difference  of  electric  level  or  electric 
pressure  in  a  circuit,  just  as  a  pump  is  a 
device  for  producing  a  difference  of  water 
level  as  in  forcing  water  into  a  reservoir. 

The  activity  of  a  reservoir,  when  dis- 
charging water,  depends  upon  the  quan- 
tity of  water  escaping  per  second;  and,  as 
in  the  case  of  all  activity,  may  be  ex- 
pressed in  foot-pounds-per-second,  or  in 


ELEMENTARY  PRINCIPLES.  35 

watts.  So  in  an  electric  circuit,  the  ac- 
tivity depends  upon  the  flow  of  electricity 
per  second  through  a  given  difference  of 
electric  level,  or  electromotive  force, 
(abbreviated  E.  M.  F.  )  and  is  also  ex- 
pressed in  joules-per-second,  or  in  watts. 
Thus,  when  100  coulombs  pass  through 
an  electric  circuit  under  a  pressure  of  50 
volts,  a  total  work  of  5000  joules  will  be 
done,  and  if  this  work  be  expended  in  one 
second,  the  activity  during  that  time  will 
be  5000  watts.  If  the  same  total  flow 
take  place  steadily  in  50  seconds,  the 
flow-per- second  would  be  2  coulombs, 
and  the  activity,  50  x  2  =  100  volt-cou- 
lombs-per -second,  or  100  watts. 

An  electric  flow  may  be  expressed  in 
coulombs-per-second;  i.  e.,  in  amperes. 
Since  an  ampere  is  a  rate  of  flow  of  one 
coulomb-per-second,  electric  activity  can 


36  ELECTRIC  HEATING. 

be  expressed  in  volt-coulombs-per-second,  or 
in  volt-amperes;  i.  e.,  in  watts.  A  circuit  in 
which  10  amperes  is  flowing  under  a  pres- 
sure of  100  volts,  is  having  electric  energy 
expended  in  it  at  the  rate  of  100  x  10 
volt- amperes,  or  1000  watts,  or  1  kilowatt. 
A  kilowatt  is  the  unit  commonly  employed 
in  the  rating  of  electrical  machinery, 
since  the  watt  is  too  small  a  unit  for  con- 
venience. One  kilowatt,  abbreviated  KW. , 
is  equal  to  1.34  H.P.,  or,  approximately, 
1J  H.P. 


CHAPTER  III. 

ELECTRICAL   HEATING   OF   BAEE   CONDUCTORS. 

THE  quantity  of  water  which  escapes 
from  a  reservoir  in  a  given  time  depends 
not  only  on  the  pressure  at  the  outlet,  but 
also  on  the  diameter  and  length  of  the 
outlet  pipe.  So,  too,  when  an  electric  cur- 
rent flows  through  a  conducting  circuit, 
the  quantity  of  electricity  which  passes 
per  second;  i.  e.,  the  coulombs-per-second, 
or  the  amperes,  depends  not  only  on  the 
pressure,  or  the  E.  M.  F.,  but  also  on 
the  length  and  dimensions  of  the  con- 
ductor, as  well  as  on  the  material  of 
which  the  conductor  is  composed,  and  on 
its  physical  condition,  such  as  hardness, 
temperature,  etc.  In  the  case  of  the  water 
pipe,  the  length  and  diameter  of  the  pipe, 


38  ELECTRIC  HEATING. 

the  nature  of  its  walls,  and  the  number 
of  its  bends,  will  determine  a  certain  liy- 
draulic  resistance,  which  will  permit  the 
flow  of  water  under  a  given  head  or  pres- 
sure through  it,  and  determine  the 
amount  which  will  escape  from  the  reser- 
voir in  a  given  time.  In  the  same  man- 
ner, in  an  electric  circuit,  the  length  and 
cross-section  of  the  conducting  wire,  or 
circuit,  taken  in  connection  with  its  nat- 
ure and  physical  conditions,  will  deter- 
mine a  certain  electric  resistance,  which 
will  permit  the  flow  of  electricity  through 
it,  under  a  given  pressure  or  E.  M.  F., 
and  determine  the  amount  of  current 
which  will  flow  through  the  circuit  in 
any  given  case. 

The  law  which  determines  the  current 
strength  in  amperes,  which  will  pass 
through  any  circuit  under  the  influence 


HEATING   OF   BARE   CONDUCTORS.          39 

of  a  given  E.  M.  F.  and  against  a  given 
resistance  in  a  circuit,  was  discovered  by 
Dr.  Ohm,  of  Berlin,  arid  is  known  as 
Ohm's  law.  This  law  may  be  stated  as 
follows:  The  current  strength  in  any 
circuit  is  equal  to  the  E.  M.  F.  acting  on 
that  circuit,  expressed  in  volts,  divided 
by  the  resistance  of  that  circuit,  expressed 
in  units  of  electrical  resistance  called 
ohms;  or  concisely,  Ohm's  law  may  be  ex- 
pressed as  follows: 

Tlie  amperes  in  any  circuit  equal  the  volts 
divided  by  the  ohms. 

For  example,  if  a  storage  cell,  with  an 
E.  M.  F.  of  two  volts,  be  connected  to  a 
circuit  whose  resistance,  including  that  of 
the  cell,  is  10  ohms,  the  current  strength 
passing  through  the  circuit  will  be  TV  =  i 
ampere;  and,  since  one  ampere  is  one  cou- 
lomb per  second,  there  would  be  flowing 
in  such  a  circuit  one -fifth  of  a  coulomb 


40  ELECTBIC   HEATING. 

per  second.  The  work  done  in  the  cir- 
cuit will  be  equal  to  the  pressure  of  two 
volts  multiplied  by  the  total  number  of 
coulombs  that  pass  in  any  given  time. 
For  example,  in  ten  minutes,  or  in  600 
seconds,  the  total  number  of  coulombs 
that  will  have  passed  through  the  circuit 
will  be  600  x  £  =  120  coulombs,  and  the 
work  expended  by  the  storage  cell  in  the 
circuit  will  be  2  x  120  =  240  volt- cou- 
lomb, or  joules,  =  177  foot-pounds.  We 
also  know  that  the  activity  in  this  circuit 
will  be  the  product  of  the  volts  and  the 
amperes,  or  2  volts  x  -j.  ampere  -  -f  watt 
f  =  joule-per-second  —  0.295  foot-pound- 
per-second. 

During  the  flow  of  water  through  a  pipe 
there  will  be  produced  a  certain  back  pres- 
su>  e,  or  counter -hydraulic  pressure,  tending 
t  j  check  the  flow  of  water  through  the  pipe. 


HEATING   OF   BARE   CONDUCTORS.  41 

In  the  same  way,  during  the  flow  of  an 
electric  current  through  a  conductor, 
there  will  be  produced  a  back  electric 
pressure,  or  counter  E.  M.  F.,  equal  in  all 
cases  to  the  E.  M.  F.  impressed  upon  the 
conductor.  In  fact,  the  current  strength 
through  the  conductor  adjusts  itself  in 
accordance  with  Ohm's  law,  in  such  a 
manner  that  the  counter  E.  M.  F.  shall 
just  be  equal  to  the  impressed  E.  M.  F. ; 
i.e.,  the  E.  M.  F.  acting  on  the  circuit. 
The  counter  E.  M.  F.  in  volts,  is  equal  to 
the  product  of  the  current  strength  in 
amperes,  by  the  resistance  of  the  conduct- 
or in  ohms.  Thus,  the  10-ohm  circuit 
above  referred  to,  carrying  a  current  of  one 
fifth  of  an  ampere,  develops  a  counter  E. 
M.  F.  of  10  x  i  =  2  volts,  which  is  just 
equal  to  the  impressed  E.  M.  F.  of  the 
cell.  The  product  of  the  current  strength 
and  the  counter  E.  M.  F.  is  the  activity 


42 


ELECTRIC   HEATING. 


expended  in  the  circuit,  just  as  the  prod- 
uct of  the   current  strength  and  the  E, 


\          /*N         /7%\         f*\         / 

>  2  OHMS 
JGERMANSILYEB 
>WIRE 

^ 

8  VOLTS         1  OHM 


TOTAL  ACTIVITY  OF' 
BATTERY  8  WATTS 


<$& 

'«£&*• 

HHH 

8  VOLTS          1  OHM 
1  AMPERES 
1  VOLT  DROP 
1  WATT  ACTIVITY 


FIG.  1.  —DISTRIBUTION  OF  C.  E.  M.  F.  IN  A  CIRCUIT. 

M.    F.    is    the    work  expended  by  the 
E.  M.  F. 

If,  for  example,  as  in  Fig.  1,  four  storage 
cells,  each  of  2  volts  E,  M,  F.  and  |  ohm 


rtt*«s 
(fy 


HEATING   OF    BAKE 

resistance,  be  connected  in  series  with  an 
external  circuit  composed  of  two  parts; 
viz.,  of  a  resistance  of  5  ohms  of  copper 
wire,  and  of  a  resistance  of  2  ohms  of 
German  silver  wire,  the  total  resistance 
of  the  circuit  will  be  8  ohms,  and  the  cur- 
rent strength  f  =  1  ampere.  The  back 
pressure,  or  drop,  in  the  German  silver 
wire  will  be  2  x  1  =2  volts.  The  back 
pressure,  or  drop,  in  the  copper  wire,  will 
be  5  x  1  =  5  volts,  and  the  activity  ex- 
pended in  each  will  be  2  volts  x  1  am- 
pere =  2  watts  in  the  German  silver  and  5 
volts  x  1  ampere  =  5  watts  in  the  copper. 

A  counter  E.  M.  F.  may  be  produced 
not  only  by  the  back  pressure  of  a  cur- 
rent passing  through  a  resistance,  but  al- 
so by  the  presence  of  certain  devices 
placed  in  the  circuit  and  operated  by  the 
current,  such,  for  example,  as  electric  mo- 


44 


ELECTEIC  HEATING. 


tors,  or  electrolytic  cells.     For  example, 
if  the  circuit  represented  in  Fig.  2  have 


i-*****"^            j*                         efc&w                       flbs*^ 

\_f\      /r\  _  /*\      ft 

TOTAL  PRESSURE  AT 
^          MOTOR  TERMINALS 
3/i  VOLTS 

8  VOLTS 


1  OHM 


TOTAL  ACTIVITY  OF 
BATTERY  6  WATTS 


OHM 


)LTS 

^AMPERE 
^  VOLT  DROP 

9ig  WATT  ACTIVITY 


2  OHMS 
1 1A  VOLTS  DROP 


FIG.  2.— DISTRIBUTION  OF  C.  E.  M.  F.  IN  A  CIRCUIT. 

its  German  silver  wire  of  2  ohms    resist- 
ance, replaced  by  a  small  electromagnetic 


HEATING  OF  BAKE   CONDUCTORS.          45 

motor  of  2  ohms  resistance,  and  two  volts 
counter  E.  M.  F.,  this  E.  M.  F.  being  de- 
veloped by  the  rotation  of  its  armature, 
then  the  current  strength  through  the 
circuit  will  be  8  volts  —  2  volts  =  6  volts 
effective  E.  M.  F.  divided  by  8  ohms  re- 
sistance =  |  =  |  ampere.  The  drop  in  the 
resistance  of  the  motor  would  be  2  x  |  = 
14  volts,  and  the  total  C.  E.  M.  F.  of  the 
motor  2  +  14  ==  34  volts.  The  total  work 
expended  in  the  circuit  by  the  storage  cell 
will  be  8  x  f  ==  6  watts,  and  the  total  ac- 
tivity absorbed  by  the  motor  will  be  34  x 
|  ==  2f  watts.  Of  this  activity  that  part 
will  be  expended  in  heat  which  is  de- 
veloped in  the  resistance  of  the  wire; 
namely,  14  x  |=  1£  watts,  and  the  remain- 
ing, or  1J  watts,  =  2  x  I  =  14  watts  will, 
disregarding  certain  losses  which  occur 
in  the  revolving  parts,  be  expended  me- 
chanically by  the  armature. 


46  ELECTKIC  HEATING. 

It  will  be  noticed,  in  the  above  case,  that 
the  activity  in  the  circuit,  which  is  the 
product  of  current  strength  and  counter 
E.  M.  F.  due  to  resistance,  is  expended  in 
heating  the  conductor,  while  the  activity 
which  is  the  product  of  current  strength 
and  counter   E.   M.    F.,   due  to  what  is 
called    magnetic    induction,    is  work  ex- 
pended     magnetically.     This     may     be 
taken  as  a  general  law ;  for,  whenever  a 
counter  E.  M.  F.  in  a  circuit  is  due  to 
thermo-electric,  chemical,  or  magnetic  ef- 
fects, the  activity  of  the  current  on  that 
C.  E.  M.  F.   is  expended  thermo- electric- 
ally,   chemically,    or    magnetically;    but 
when  the  C.  E.  M.  F.  is  merely  that  due 
to  the  drop  of  pressure  in  the  conductor, 
the  activity  in  this  drop  is  expended  as 
thermal  activity. 

Consequently,  when  an  electric  source, 


HEATING  OF  BABE  CONDUCTOES.  47 

such  as  a  dynamo -electric  machine,  is 
connected  to  a  circuit,  the  counter  E.  M. 
F.  of  the  external  circuit  must  be  equal 
to  the  pressure  or  E.  M.  F.  of  the  dynamo 
at  its  terminals.  The  greater  the  propor- 
tion of  this  counter  E.  M.  F.  due  to  mag- 
netic induction,  or  to  chemical  effect,  the 
greater  will  be  the  activity  expended  in 
the  circuit  as  magnetic,  or  as  chemical 
activity,  while  the  remainder,  due  to 
drop  in  pressure,  or  the  resistance  of 
the  circuit,  will  be  expended  thermally 
in  heating  the  conductor.  When,  there- 
fore, a  motor  is  connected  to  the  terminals 
of  a  dynamo,  the  efficiency  of  the  motor 
will  increase  with  the  proportion  of 
the  counter  E.  M.  F.  due  to  the  rotation 
of  the  armature;  whereas,  if  instead  of 
obtaining  mechanical  work  from  the 
motor  we  wish  to  produce  as  much  heat 
as  possible  in  the  circuit,  we  cause  the 


48  ELECTBIC  HEATING, 

motor  bo  come  to  rest,  so  that  all  the 
electrical  activity  will  be  expended  in  the 
drop  of  pressure  which  will  then  con- 
stitute the  entire  counter  E.  M.  F. 

The  resistance  of  any  wire  depends 
upon  its  resistivity,  (or  the  resistance  of  a 
cubic  centimetre  measured  between  op- 
posed faces)  its  length,  and  its  area  of 
cross-section  (1  in.  =  2.54  centimetres. 
1  sq.  in.  =  6.4516  square  centimetres.  1 
cu.  in.=  16.387  cubic  centimetres.) 

The  following  is  a  table  of  resistivities 
of  the  more  important  metals  expressed 
in  microhms,  or  millionths  of  an  ohm,  for 
a  temperature  of  0°  C.,  the  freezing  point 
of  water: 

TABLE  OF  RESISTIVITIES. 

Substance.  "Resistivity. 

Silver,  annealed,  .  .  .  1.500  microhms. 
Silver,  hard  drawn,  .  1.53 


HEATING  OF  BAKE  CONDUCTOES.    49 

Copper,  annealed, 
(Matthiessen's 

standard)  ....  1.594      microhms. 
Copper,  hard  drawn,  1.629 
Iron,  annealed,  .  .  .  9.687  " 

Nickel,  annealed,  .   12.420  " 

Mercury,  liquid,  .  .     94.84  " 

German  silver,  about  20.9 
The  reference  to  a  standard  temperature 
is  necessary,  in  a  table  of  resistivities,  be- 
cause the  resistivity  usually  varies  ap- 
preciably with  variations  in  the  tem- 
perature. Thus,  the  resistivity  of  pure 
soft  copper  is  given  as  1.594  microhms  at 
0D  C.  and  this  means  that  the  resistance 
between  any  such  pair  of  opposed  faces 
as  a  and  6,  in  a  block  of  this  copper 
one  centimetre  cube,  as  represented  at 
A,  in  Fig.  3,  would  have  a  resistance 
of  1.594  microhms,  or  T^^nr  ohms. 


50 


ELECTRIC   HEATING. 


If  a  wire  having  a  cross -section  of  1  sq. 
cm.  as  a1,  at  B  in  Fig  3,  have  a  length  of  5 
cms.,  then  the  resistance  between  the 
terminal  faces  a1  and  b\  will  be  5  times 
as  great  as  between  the  terminal  faces  of 
the  cube  at  A,  in  the  same  figure,  or  5  x 


FIG.  3.— DIAGRAM  REPRESENTING  RELATION  BETWEEN  RE- 
SISTIVITY AND  RESISTANCE. 

1.945  =  7.97  microhms.  Again,  if  the  wire 
were  5  centimetres  ]ong,  and  had  a  cross - 
section  of  three  square  centimetres,  as 
shown  at  C,  in  Fig.  3,  then  each  centime- 
tre length  of  such  wire  would  have  one- 
third  the  resistance  of  the  unit  cube,  or 


HEATING   OF   BARE   CONDUCTORS.  51 

l-53-—  =  0.533  microhm,  and  the  total  re- 
sistance between  the  terminal  faces  a" 
and  b\  would  be  0.533  x  5  =  2.657  mi- 
crohms. In  all  cases,  therefore,  with  a 
wire  of  uniform  material,  temperature 
and  resistivity,  it  is  only  necessary  to 
multiply  the  resistivity  by  the  length  in 
cms.  and  divide  by  the  cross-sectional 
area  of  the  wire  in  square  centimetres,  to 
obtain  the  total  resistance  of  the  wire. 

While  the  preceding  is  a  fundamental 
relation,  yet,  in  practice,  it  is  not  always 
necessary  to  determine  the  cross -section 
of  the  wire  in  square  centimetres,  and  its 
length  in  centimetres,  in  order  to  com- 
pute its  resistance.  In  English-speaking 
countries  it  is  customary  to  express  the 
diameter  of  a  wire  in  thousandths  of  an 
inch,  or  in  mils,  one  mil  being  the  one- 
thousandth  of  an  inch.  If  we  square  the 


52  ELECTRIC  HEATING. 

number  of  mils  in  the  diameter  of  a  wire 
we  obtain  the  number  of  what  is  called 
circular  mils  in  the  wire.  Thus,  if  a  wire 
have  a  diameter  of  one-tenth  of  an  inch 
=  100  mils,  the  number  of  circular  mils 
in  the  cross -section  of  this  wire  will  be 
100  x  100  =  10,000  circular  mils.  A  wire 
one  inch  in  diameter  would  have  a  cross - 
section  of  one  million  circular  mils. 

The  resistance  of  a  pure  standard  copper 
wire  one  foot  long,  and  one  circular  mil 
in  cross-section,  is  10.35  ohms,  at  20°  C., 
that  is  to  say,  a  wire  one -thousandth  of 
an  inch  in  diameter  and  one  foot  lo:_^ 
would  have  this  resistance.  The  re- 
sistance-per -foot  in  any  pure  copper  wire 
will  be  this  resistance,  divided  by  the 
number  of  circular  mils  in  its  cross -sec- 
tion. For  example,  the  wire  above  re- 
ferred to  as  having  10,000  circular  mils 
in  its  area  of  cross -section  would  have 


HEATING  OF  BAKE  CONDUCTORS.          53 

a  resistance  per-foot  of  TV>3oV  =:  0.001035 
ohm-per-foot  at  20°  C.  The  resistance  of 
such  a  wire  per  mile  would  be  5*280  x 
0.001035  =  5.465  ohms. 

While  the  use  of  circular  mils  Is  very 
convenient  for  wires  whose  length  is  ex- 
pressed in  feet,  when  tables  or  data  con- 
cerning the  resistance  of  a  circular-mil- 
foot  have  been  prepared,  yet  it  is  desira- 
ble to  retain  also  the  fundamental  con- 
ception of  the  resistance  as  dependent 
upon  resistivity  and  dimensions  for  the 
cases  which  may  occur  that  are  not 
dealt  with  in  tables.  For  example,  a  re- 
sistance of  100  metres  (10,000  cms.)  of  pure 
soft  copper  wire  at  0°  C.  having  a  cross- 
section  of  0.05  square  centimetre  would 
be — 1..JL9.4  *.i_o^o_o  microhms  =  318,800  mi- 
crohms =  0.3188  ohm. 


54  ELECTRIC   HEATING. 

The  resistivity  of  a  metal  is  always  re- 
duced by  the  process  of  softening  or  an- 
nealing it,  although  the  reduction  in  the 
resistivity,  due  to  annealing,  may  only 
amount  to  one  or  two  per  cent.  The  re- 
sistivity depends  very  greatly,  however, 
upon  the  physical  nature  and  purity  of 
the  material.  A  very  small  percentage  of 
certain  impurities  in  a  copper  wire,  such, 
for  example,  as  phosphorus  or  sulphur, 
will  greatly  increase  its  resistivity,  and 
even  the  presence  of  gases  occluded  or 
absorbed  by  the  substance  of  the  wire  is 
said  to  appreciably  increase  its  resistivity. 
The  purity  with  which  copper  wires  can 
be  commercially  obtained,  at  the  present 
time,  is  such  that  their  resistivity  is,  per- 
haps, only  one  per  cent,  greater  than  that 
of  the  so-called  pure,  standard,  soft-cop- 
per wire,  while  it  sometimes  happens  that 
wires  are  obtained  commercially  whose 


HEATING   OF 


resistivity    is 
this  standard. 


In  dealing  with  wires  of  other  metals 
than  copper,  such  as  lead,  iron  and  Ger- 
man silver,  the  tabular  resistivities  can- 
not, as  a  rule,  be  relied  upon  to  limits 
closer  than  say  five  per  cent.,  and  where  a 
degree  of  accuracy  greater  than  this  is  re- 
quired, measurements  of  the  resistivity  of 
such  wires,  at  a  given  temperature,  are 
necessary.  This  can  be  done  by  carefully 
measuring  the  resistance  of  a  given  length 
of  wire  when  its  cross-section  is  known  or 
can  be  carefully  observed.  The  resistiv- 
ity in  ohms,  at  the  temperature  of  the 
measurement,  will  then  be  the  resistance 
multiplied  by  the  cross- sectional  area  of 
the  wire  in  square  centimetres  divided 
by  the  length  of  the  wire  in  centimetres. 


56  ELECTBIC   HEATING. 

The  effect  of  temperature  on  all  pure 
metallic  conductors  is  to  increase  the  re- 
sistivity. Nearly  all  alloys  also  increase 
in  their  resistivity  with  increase  in  tem- 
perature, though  less  rapidly  than  their 
pure  component  metals.  A  few  specially 
prepared  alloys,  such  as  platinoid,  have  a 
very  small  increase  of  resistivity  with 
temperature,  and  are,  therefore,  in  special 
request  for  the  manufacture  of  permanent 
resistance  coils,  whose  resistances  are  to 
remain  as  nearly  constant  as  possible; 
while  one  or  two  alloys  have  been  pre- 
pared whose  resistivities  are  either  not 
effected  by  temperature,  or  have  a  slight 
positive  or  negative  coefficient;  i.  e.  ,  a 
slight  increase  or  decrease  in  resistivity 
with  temperature,  at  different  points  of 
the  thermometric  scale.  Carbon  di- 
minishes in  resistivity  about  0.5  per  cent, 
per  degree  centigrade,  reckoned  from  its 


HEATING  OF  BARE  CONDUCTORS.     57 

resistivity  at  zero  centigrade.  Pure 
metals,  or  metals  containing  only  a  very 
small  percentage  of  impurity,  usually  in- 
crease about  0.4  per  cent,  in  their  resistiv- 
ity, per  degree  centigrade,  above  that 
which  they  possess  at  zero  centigrade. 
For  example,  taking  the  resistivity  of  cop- 
per as  1.594  microhms  at  0°C,  its  resis- 
tivity at  20°  C.  will  be  increased  by  20 
x  0.4=8  per  cent.,  so  that  its  resistivity  at 
this  temperature  will  be  1.594  x  £££= 
1.721  microhms,  approximately.  At  the 
boiling  point  of  water,  or  100°  C.,  its  re- 
sistivity will  have  become  increased  by 
approximately  100  x  0.4  —  40  per  cent., 
and  its  resistivity  will  be  ±'J***±±s.  =  2.232 
microhms. 

When  the  resistivity  of  a  wire  is 
known,  either  by  actual  measurement  at 
the  temperature  of  observation,  or  from 


58  ELECTEIC   HEATING. 

its  tabular  resistivity  at  (PC.  referred 
as  above  to  the  actual  temperature,  the 
amount  of  heat  which  will  be  developed 
in  it  in  a  given  time,  by  a  given  current 
strength,  becomes  known,  except  in  so 
far  as  its  temperature  elevation  under  the 
heating  influence  may  be  undetermined. 
For  example,  if  a  copper  wire  were  insu- 
lated by  a  thin  coating  of  some  non-con- 
ducting varnish  and  placed  in  ice -water 
at  0°  C.,  the  resistivity  of  the  wire  might 
be  1.6  microhms,  and  a  circular -mil -foot 
of  this  wire  would  have  a  resistance  of 
9.625  ohms.  If  the  diameter  of  the  wire 
were  0.01";  i.  e. ,  No.  30  of  the  American 
wire  gauge  (A.W.G.)  having  a  cross-sec- 
tion of  100.5  circular  mils,  the  resistance 
of  10  feet  of  such  wire  would  be  -VoTi6!-- 
=0.9577  ohms  at  0°  C.  If  a  current  of  two 
amperes  be  sent  steadily  through  this 
length  of  wire,  the  drop  in  the  wire  would 


HEATING  OF  BARE  CONDUCTORS.     59 

be  2  x  0.9577=1.9154  volts,  and  the  activ- 
ity expended  thermally  in  the  wire  would 
be  2  x  1.9154=3.831  watts,  or  joules-per- 
second  =:  2.827  foot-pounds-per-second. 
The  heat  which  would  be  expended  in  the 
wire  would  fail  to  appreciably  raise  its 
temperature,  since  it  would  readily  pass 
through  the  insulating  varnish  into  the 
ice-water,  and,  if  we  assume  that  abun- 
dant ice  is  present,  the  temperature  of 
the  water  would  not  be  raised  until  all  the 
ice  was  melted.  The  work  done  by  the 
electric  source  in  supplying  the  current 
through  this  wire  would,  therefore,  be 
expended  in  melting  the  ice. 

If,  however,  the  same  length  of  wire  be 
suspended  in  air,  and  the  same  current 
strength,  of  say  2  amperes,  passes  stead- 
ily through  it  as  before,  then,  although 
some  of  the  heat  would  be  carried  off  by 


60  ELECTRIC   HEATING. 

the  air,  yet  the  resistance  offered  by  the 
air  to  the  escape  of  the  heat  from  the  wire 
would  be  much  greater  than  that  offered 
by  the  varnish  and  water  in  the  preceding 
case,  so  that  the  temperature  of  the  wire 
would  be  raised.  This  would  increase 
the  resistivity  of  the  wire  at  the  rate  of, 
approximately,  0.4  per  cent,  per  degree 
centigrade  of  temperature  elevation,  so 
that  both  the  resistance  and  the  thermal 
activity  of  the  wire  would  rise. 

Suppose,  for  example,  that  the  air  sur- 
rounding the  wire  is  at  a  temperature  of 
20°  C.  and  that  the  current  through  the 
wire  raises  its  temperature  10°C.  above 
the  surrounding  air,  or  to  30°  C.  Then 
the  resistivity  of  the  wire  before  the 
current  passed  through  it,  would  be 
1.6  x  |£|=  1.728  microhms,  and  after 
the  current  has  passed  through  it  steadily 
1.6  x  }±%  =  1.792  microhms,  so  that  the 


HEATING  OF  BAKE  CONDUCTORS.        61 

resistance  of  the  heated  wire  will  be  10.72 
and  the  thermal  activity  in  the  heated 
wire  4.288  watts. 

It  is,  therefore,  a  simple  matter  to  de- 
termine the  thermal  activity  in  a  given 
conductor  when  the  drop  of  pressure  in 
the  conductor  and  the  current  strength 
passing  through  it  are  observed;  for,  if  the 
drop  in  a  wire,  for  example,  be  5  volts, 
and  the  current  through  the  wire,  100 
amperes,  then  the  thermal  activity  in  the 
wire  will  be  500  watts.  But  it  is  by  no 
means  a  simple  matter  to  determine  what 
temperature  the  wire  will  attain  when 
subjected  to  this  heating,  since  the  wire 
is  constantly  losing  its  heat  at  a  rate  which 
depends  upon  a  variety  of  circumstances. 

When  a  current  passes  through  a  wire, 
the  heat  developed  by  that  current  causes 


62  ELECTRIC   HEATING. 

it  to  increase  its  temperature.  When  a 
body  is  heated  above  the  temperature  of 
surrounding  bodies,  •  heat  flows  from  the 
former  to  the  latter,  just  as  water  flows 
from  a  higher  to  a  lower  level.  The  great- 
er the  elevation  of  temperature  of  the 
heated  body,  the  more  rapid  will  be  the 
passage  of  heat,  or  the  greater  the  thermal 
current  strength.  When  the  body  is  sup- 
plied with  heat  at  a  steady  rate,  its  tem- 
perature continues  to  rise  until  the  rate 
at  which  it  receives  heat  is  balanced 
by  the  rate  at  which  it  loses  it.  Conse- 
quently, a  time  is  reached  when  the  tem- 
perature of  the  body  remains  constant, 
although  the  body  is  constantly  receiv- 
ing heat.  When,  therefore,  an  electric 
current  has  been  passing  for  a  sufficient 
length  of  time  through  a  conductor,  its 
temperature  will  attain  a  definite  eleva- 
tion above  that  of  surrounding  bodies  and 


HEATING   OF   BARE   CONDUCTORS.  63 

remain  constant,  the  thermal  activity 
within  the  conductor  being  balanced  by 
the  loss  of  heat  from  the  surface  of  the 
conductor. 

Heat   escapes    from  a  body   in   three 
ways ;    namely, 

(1)  By  conduction  to  bodies  in  imme- 
diate contact  with  its  surface;  as,  for  ex- 
ample, when  a  heated  wire  is  enclosed  in 
a  mass  of  lead  or  rubber,  the  heat  passing 
directly  across  the  surface  of  the  wire 
into  the  surrounding  substance. 

(2)  By  convection,  which  occurs  only  in 
fluids;  i.e.,  liquids  or  gases.     Here,  the 
particles  of  fluid  surrounding  the  hot  body 
become  heated  and  are  carried  through 
the  fluid  mass  by  currents,  set  up  by  dif- 
ferences in  density  of  the  hotter  and  cool- 
er portions  of  the  fluid. 

(3)  By  radiation,  the  heat  passing  out 


04  ELECTKIO  HEATItfG. 

from  the  heated  surface  in  straight  lines 
just  as  light  does,  when  a  body  becomes 
incandescent. 

As  to  which  of  the  above  methods  of 
loss  of  heat  is  the  most  effective  in  the 
case  of  a  wire  heated  by  an  electric  cur- 
rent, depends  upon  the  character  of  the 
surroundings  of  the  wire,  whether  the 
wire  is  bare  or  covered,  and  where  it  is 
placed. 

Circuit  wires  may  be  either  bare  or  cov- 
ered. Bare  wires  are  only  suitable  for 
suspension  in  air.  Covered  wires  may  be 
placed  in  air,  in  water,  or  in  the  ground. 
The  character  of  the  covering  may  also 
vary  in  different  cases. 

It  might  be  supposed  that  a  bare  wire 
suspended  in  the  air  was  the  simplest 
case  to  deal  with.  Such,  however,  is  far 


HEATING  OF  BARE  CONDUCTORS.          65 

from  being  the  case;'  for  not  only  does  the 
position  of  the  wire  itself  greatly  affect 
the  ease  with  which  it  loses  heat,  but  al- 
so the  condition  of  the  surrounding  air, 
whether  at  rest  or  in  motion. 

When  a  bare  wire  is  supported  horizon- 
tally in  the  air  of  a  room,  and  an  electric 
current  is  passed  through  it,  this  current 
will  set  up  a  certain  drop  of  pressure  in 
the  wire,  and  the  product  of  this  drop  and 
the  current  strength,  will  give  the  thermal 
activity  developed  in  the  wire  at  the  out- 
set. 

Under  these  circumstances  the  tem- 
perature elevation  of  the  wire  will  have 
become  practically  constant  in  about  two 
minutes.  As  soon  as  this  limiting  tem- 
perature is  reached  the  heat  developed 
by  the  electric  current  in  any  length  of  the 
wdre,  such  as  an  inch  or  a  centimetre,  will 
be  equal  to  the  heat  dissipated  from  its 


66  ELECTRIC  HEATING. 

surface  by  radiation  and  convection.  The 
amount  of  heat  that  will  be  radiated  in  a 
given  time,  say  one  second,  from  a  given 
length  of  the  wire,  say  one  inch,  will  de- 
pend upon  the  extent  of  free  surface  of  the 
wire  in  that  length,  upon  the  nature  of 
its  surface,  whether  bright,  blackened  or 
colored,  smooth  or  rough,  etc.,  and  upon 
the  temperature  elevation  the  wire  has 
attained.  A  rough,  blackened  surface  will 
radiate  heat,  approximately,  twice  as  rap- 
idly as  a  smooth,  bright  surface. 

The  heat  which  will  escape  from  the 
wire  by  convection,  in  the  same  length, 
so  far  as  is  known,  is  practically  the 
same  for  all  diameters  of  wire  and  for  all 
characters  of  surface,  so  that  the  loss  by 
convected  heat  does  not  depend  upon  the 
surface,  or  only  increases  slightly  with 
the  surface,  while  the  loss  by  radiated 


HEATING   OF   BAKE   CONDUCTORS.          67 

heat  increases  directly  with  the  surface. 

For  every  degree  centigrade  of  tem- 
perature elevation  attained  by  the  wire 
above  the  surrounding  still  air  of  a  room, 
the  heat  lost  by  convection  is,  approxi- 
mately, 0.053  joules-per-second,  per  foot  of 
length,  so  that  if  the  wire  has  a  temper- 
ature elevation  of  20°  C. ,  every  foot  will 
lose  by  convection,  approximately,  1.06 
joules-per-second,  or  will  lose  heat  energy 
at  the  rate  of  1.06  watts.  The  loss  by 
radiation  will  be  approximately  0.004  watt 
per  square  inch  of  bright  surface,  per  de- 
gree centigrade  of  temperature  elevation. 

The  total  loss  of  heat  in  watts  will, 
therefore,  be  the  temperature  elevation  of 
the  wire,  in  degrees  centigrade,  multiplied 
by  the  number  of  feet,  and  by  0.053  for  the 
effective  loss  and  the  same  temperature 


68  ELECTKIC  HEATING. 

elevation  multiplied  by  the  number  of 
square  inches  of  surface  and  0.004  for 
the  radiation  loss. 

When  the  air,  in  which  a  wire  carrying 
an  electric  current  is  suspended,  is  in  a 
state  of  motion,  as,  for  example,  when  the 
wire  is  suspended  out  of  doors,  and  ex- 
posed to  wind  and  air  currents,  the  loss 
of  heat  by  convection  from  its  surface  is 
greatly  increased  even  in  the  calmest 
w^eather.  Air  currents  carry  off  a  large 
amount  of  heat  from  the  wire,  so  that  the 
temperature  elevation  of  the  wire  for  a 
given  current  strength  is  considerably  re- 
duced. 


CHAPTER  IV. 

ELECTRICAL      HEATING      OF      COVERED      CON- 
DUCTORS. 

AN  electric  conductor,  when  employed 
to  carry  an  electric  current  to  a  distance, 
is  intended  to  be  kept  as  cool  as  possible; 
first,  because  a  hot  wire  necessarily 
means  a  wire  in  which  energy  that  might 
otherwise  be  utilized  is  being  expended 
uselessly  as  heat;  second,  because  the  re- 
sistance of  a  hot  wire  is  higher  than  that 
of  a  cold  wire  and,  consequently,  more 
energy  is  wasted  in  the  wire  to  sustain  a 
given  current;  and  third,  because  a  wire 
that  is  overheated  by  the  current  it  car- 
ries, may  either  destroy  its  insulation  or 
set  fire  to  inflammable  bodies  in  its  vicin- 
ity. On  the  contrary,  an  electric  conduct- 


70  ELECTRIC   HEATING. 

or,  which  is  intended  for  purposes  of  de- 
veloping heat  by  the  expenditure  of  elec- 
tric energy,  as  in  an  electric  heater,  is  do- 
ing its  best  service  when  it  is  as  hot  as  it 
can  become  without  danger  of  injury  from 
an  excessive  temperature.  Since  the 
great  majority  of  heated  electric  conduct- 
ors are  those  in  which  heat  is  both  an  ob- 
jection and  a  loss,  it  is  necessary  to  ex- 
amine the  laws  which  control  their  heat- 
ing, with  a  view  of  avoiding  a  dangerous- 
ly high  temperature. 

Whether  a  covered  wire  be  supported 
in  air,  buried  in  the  ground,  or  immersed 
in  water,  it  is  evident  that  its  heat  must 
first  escape  into  the  insulating  covering, 
before  it  can  pass  into  the  surrounding 
medium.  In  other  words,  the  insulat- 
ing covering  offers  a  certain  resistance  to 
the  escape  of  heat  from  the  wire,  and,  if 


HEATING   OF    COVERED 

the  covering  could  be  r  erased  "without 
allowing  the  electricity  to  escapeHfrom 
the  wire,  the  temperature  of  the  wire, 
under  any  given  current  strength,  would 
be  less  than  that  it  attains  with  the  cover- 
ing in  place. 

The  thermal  resistance  of  any  insulating 
covering,  on  a  round  wire,  depends  on  the 
proportion  of  the  diameter  of  the  bare 
conductor  to  the  diameter  of  the  covered 
conductor,  and  on  the  nature  of  the  insu- 
lating material.  As  no  two  insulating 
coverings  offer  exactly  the  same  electric 
resistance  to  the  escape  of  electricity,  so 
no  two  insulating  coverings  offer  exactly 
the  same  thermal  resistance  to  the  es- 
cape of  heat  from  the  wire.  All  good 
electric  insulators  are  good  thermal  non- 
conductors, so  that  just  as  a  considerable 
difference  of  electric  pressure  is  required 


72  ELECTRIC   HEATING. 

to  force  a  given  quantity  of  electricity 
through  a  conducting  coating  on  a  wire, 
so  a  considerable  difference  of  thermal 
pressure;  i.e.,  difference  of  temperature, 
is  required  between  the  inside  and  outside 
of  the  coating  to  force  a  given  quantity  of 
heat  through  the  coating.  When,  therefore, 
the  insulating  coating  is  thick,  it  is  to  be 
expected  that  the  temperature  elevation 
of  the  wire,  for  a  moderate  current 
strength,  will  be  appreciable.  If,  how- 
ever, the  covered  wire  be  supported  in  the 
air  of  a  room,  it  will  frequently  happen 
that  the  wire  will  be  cooler  than  if  devoid 
of  covering,  for  the  reason  that  the  advan- 
tage gained  by  increased  external  surface 
and  the  greater  radiation  therefrom,  will 
more  than  compensate  for  the  additional 
thermal  resistance  between  the  surfaces 
of  the  wire  and  the  air  surrounding  it. 
The  same  is  also  more  likely  to  be  the 


HEATING   OF   COVERED   CONDUCTORS.          /  6 

case  if  the  insulating  covering  of  the  wire 
be  blackened,  since  its  radiation  will  there- 
by be  increased. 

When  a  covered  wire,  instead  of  being 
supported  in  air,  is  immersed   in  water, 
the  temperature  elevation  of  the  wire  is 
increased  by  reason  of  the  insulating  cov- 
ering; for,  if  the  wire  could  be  covered 
with  a  very  thin,   electrically  non-con- 
ducting varnish,  it  would  be  almost  im- 
possible to  raise  the  temperature  of  the 
conductor,  so  rapid  is  the  communication 
of  heat  from  the  metal  to  the  mass  of 
surrounding    liquid,     and    so    slow    the 
elevation  of  temperature  in  the  liquid,  if 
its  volume  is  large.    With  air,  as  we  have 
seen,    the    case    is    very    different;     the 
thermal    resistance  of  still  air  is  often 
large,    while    the  thermal  resistance  of 
water  is  very  small.     With  wires  sub- 


74  ELECTKIC  HEATING. 

merged  in  water  it  may  be  safely  assumed 
that  the  entire  thermal  resistance  to  the 
escape  of  heat  exists  in  the  non-conduct- 
ing covering,  and  that  no  thermal  resist- 
ance exists  in  the  water  outside  it. 

A  covering  of  metal  on  the  external 
surface  of  an  insulated  wire,  such,  for  ex- 
ample, as  a  thin  shell  of  lead  spread  over 
the  insulating  material,  does  not  offer  any 
appreciable  thermal  resistance.  Metals 
conduct  heat  so  rapidly,  as  compared  with 
insulating  substances,  that  the  thermal 
resistance  in  the  metal  may  be  neglected. 
In  fact  a  lead  sheath  aids  in  cooling  a  wire 
suspended  in  air,  since  it  provides  an  in- 
creased surface  for  loss  of  heat  by  radia- 
tion and  convection;  or,  in  other  words,  it 
reduces  the  effective  thermal  resistance 
of  the  air. 


HEATING   OF   COVERED   CONDUCTORS.       /O 

The  safe  carrying  capacity  of  a  conductor 
may  be  defined  as  the  current  strength 
that  can  safely  be  permitted  to  pass 
through  it.  The  carrying  capacity  de 
pends  upon  the  highest  limit  of  tempera- 
ture elevation  permitted  as  consistent  with 
safety.  In  some  cases,  it  is  desirable, 
from  considerations  of  economy  of  in- 
stallation, to  press  the  electric  activity  of 
a  wire  up  to  the  limit  of  safety.  In  most 
cases,  however,  it  is  too  expensive  to  force 
the  activity  of  a  wire  to  such  a  limit,  for 
the  reason  that  the  expense  of  the  thermal 
activity  expended  in  the  wire,  at  the 
safety  limit,  renders  a  larger  and  more 
costly  wire,  with  a  lower  resistance  and 
diminished  temperature  elevation,  eco- 
nomical. In  cases  where  it  is  desirable  to 
carry  a  powerful  current  with  the  mini- 
mum cross -section  or  weight  of  conductor 
consistent  with  safety,  it  is  often  advan- 


76  ELECTKIC   HEATING. 

tageous  to  subdivide  the  conductor;  i.  e., 
to  employ  two  or  more  small  wires  in- 
stead of  a  large  single  conductor.  In  the 
case  of  a  subdivided  conductor,  the  tem- 
perature elevation  of  each  separate  wire 
will  be  considerably  less  than  the  tem- 
perature elevation  of  a  single  wire  carry- 
ing the  entire  current.  This  is  for  the 
reason  that  the  surface  of  a  pound  of  a 
given  wire  varies  with  its  area  of  cross- 
section,  decreasing  as  the  area  of  cross- 
section  increases,  and  vice  versa.  In 
other  words,  a  small  wire  has  a  larger 
surface,  per  pound,  than  a  large  one,  and, 
as  is  evident,  the  greater  the  surface, 
the  greater  the  rapidity  with  which  the 
heat  generated  within  the  substance  of 
the  wire  can  escape. 

An  insulated  wire  placed  in  a  wooden 
moulding,  or  in  a  closely -fitting  conduit  in 


HEATING   OF  COVEKED   CONDUCTORS.      77 

a  building,  loses  its  heat  entirely  by  con- 
duction, provided  the  walls  of  the  panel 
or  conduit  are  everywhere  in  contact 
with  the  external  surface  of  the  covered 
wire.  In  this  case,  the  temperature  ele- 
vation of  the  wire,  for  a  given  current,  is 
greater  than  if  the  wire  were  immersed 
in  water,  since  the  thermal  resistance  of 
the  walls  of  the  panel  is  added  to  the 
thermal  resistance  of  the  insulating  cover- 
ing. In  almost  all  cases,  however,  the 
temperature  elevation  is  less  than  if  the 
wire  were  supported  in  air.  Consequent- 
ly, the  effective  thermal  resistance  of  a 
panel  or  conduit,  is  generally  less  than 
the  effective  thermal  resistance  of  the 
air  within  a  room. 

The  rule  in  common  use  for  determin- 
ing the  size  of  wires  to  be  placed  in 
wooden  mouldings,  is  to  allow  1000  am- 
peres per  square  inch  of  area  of  cross- 


78  ELECTEIC   HEATING. 

section.  This  rule  is  easily  applied,  and 
affords  a  convenient  guide  in  the  absence 
of  any  special  tables  of  reference.  It 
must  be  remembered,  however,  that  the 
rule  implies  that  a  large  wire  will  lose  its 
heat  as  readily  as  a  small  one,  and  this, 
as  we  have  seen,  is  not  the  case,  owing 
to  the  reduction  of  surface  per  unit  of 
cross- sectional  area  or  weight.  Conse- 
quently, a  very  large  wire,  selected  accord- 
ing to  this  rule,  would  be  heated  to  a  much 
higher  temperature  than  a  very  small 
wire.  In  fact,  the  rule  is  not  to  be  re- 
garded as  entirely  safe  beyond  250  am- 
peres of  current  strength. 

In  buildings  which  are  not  absolutely 
fir  epi'oof ,  it  is  important  that  the  conduct- 
ors, which  may  be  placed  in  them  for 
supplying  electric  light  or  power,  shall 
be  so  proportioned  that  their  temperature 
may  never  become  dangerously  high.  A 


HEATING   OF   COVERED    CONDUCTORS.      79 

wire  which  can  be  grasped  in  the  hand, 
say  for  a  minute,  without  marked  discom- 
fort from  its  heat,  may  be  regarded  as  at 
a  safe  temperature.  The  limiting  tem- 
perature, defined  in  this  way,  will  of  course 
depend  physiologically  upon  the  condition 
of  the  hand  and  the  sensibility  of  the  per- 
son making  the  experiment,  but  roughly, 
may  be  considered  as  in  the  neighborhood 
of  50°  C.  If  we  assume  that  the  summer 
temperature  of  the  interior  of  a  house  is 
30°  C.  or  86°  F.,  then  to  conform  with  these 
requirements  as  to  temperature,  the  limit- 
ing temperature  elevation  for  such  a  wire 
would  be  fixed  as  approximately  20°  C. 
In  other  words,  we  must  not  allow  the 
current  strength  through  the  wire  to  ex- 
ceed that  necessary  to  elevate  its  temper- 
ature 20° C.,  since,  otherwise,  in  summer, 
the  temperature  attained  by  the  wire  at 
full  load  would  exceed  50°  C.  In  practice, 


80  ELECTRIC  HEATING. 

however,  the  limiting  temperature  allowed 
by  Fire  Insurance  Boards  is  sometimes 
placed  as  low  as  10°  C.  at  full  load,  so  as 
to  allow  margin  for  any  accidental  over- 
loads that  may  occur  unexpectedly. 

If  we  double  the  current  strength  pass- 
ing through  a  wire,  under  any  given  con- 
ditions, we  quadruple,  roughly,  the  tem- 
perature elevation  of  the  wire.  Thus,  if 
a  wire  in  moulding  be  elevated  10°  C. 
above  surrounding  temperatures  by  the 
passage  of  its  full -load  current,  then 
twice  that  current  strength  will  elevate  its 
temperature  40°  C.,  approximately,  or  72° 
F.,  and  if  the  wire  be  originally  at  a  tem- 
perature of  78°  F.,  its  final  temperature 
with  double  full  load  will  be  150°  F, 

Insulated  wire  for  underground  work 
usually  possesses  in  addition  to  the  ordi- 


HEATING   OF   COVERED    CONDUCTORS.       81 

nary  insulating  material,  a  sheathing  of 
lead,  and  is  either  buried  directly  in  the 
ground,  or  is  placed  in  a  conduit.  The  ne- 
cessity for  obtaining  a  ready  access  to 
wires  for  their  examination  has  led  to  the 
latter  process  being  adcrpted  in  most  cases. 
In  order  to  insure  high  insulation,  the  con- 
duits frequently  have  air  forced  through 
them,  in  which  case  their  condition  ap- 
proximates to  that  of  a  lead -covered 
wire  supported  in  air. 

Taking  now  the  case  of  a  wire  buried 
directly  in  the  ground,  the  thermal  resist- 
ance to  the  escape  of  heat  from  the  con- 
ductor is  not  only  that  of  the  insulator, 
but  also  that  of  the  ground.  If  the  ground 
be  moist,  its  effective  thermal  resistance  is 
reduced,  but  if  it  be  dry,  the  thermal  re- 
sistance may  be  considerable.  In  almost 
all  cases,  however,  the  thermal  resistance 


82  ELECTRIC  HEATING. 

of  the  ground  is  less  than  the  thermal  re- 
sistance of  still  air,  so  that  a  buried  wire, 
carrying  a  given  current  strength,  will  be 
cooler  than  the  same  wire  supported  in 
still  air,  although  cases  may  occur  in 
which  this  statement  does  not  hold  good. 

Intermediate  between  the  condition  of 
a  wire  suspended  in  the  air  of  a  room, 
and  a  wire  in  a  conduit,  in  which  there  is 
no  attempt  at  forced  ventilation,  there  is 
the  condition  of  a  wire  supported  in  a  sub- 
way. Here  the  air  being  at  rest,  the  con- 
ditions approximate,  thermally  at  least,  to 
the  case  of  a  wire  in  the  still  air  of  a  room. 

When  a  wire  has  been  electrically  in- 
active for  a  considerable  period  of  time, 
its  temperature  will  necessarily  coincide 
with  that  of  the  surrounding  air  or  other 
material.     When,  however,  the  full-load 


HEATING   OF   COVERED    CONDUCTORS.      83 

current  is  sent  through  the  wire,  its  tem- 
perature will  immediately  begin  to  rise, 
the  rate  of  elevation  of  temperature  being 
a  maximum  at  the  outset,  and  diminish- 
ing steadily  as  elevation  of  tempera- 
ture is  attained.  From  a  theoretical  stand- 
point the  wire  never  does  reach  the  full 
maximum  temperature,  but  always  ap- 
proaches it.  Practically,  however,  a  wire 
in  air,  reaches,  say  95  per  cent,  of  its  maxi- 
mum temperature  in  two  minutes  after 
the  application  of  the  full -load  current 
strength.  In  water  a  wire  reaches  this 
temperature  in  about  ten  minutes  after 
the  full-load  current  is  applied;  in  wood- 
en moulding,  in  about  fifteen  minutes, 
and,  when  buried  in  the  ground,  in  about 
twenty  minutes.  The  larger  the  wire, 
the  greater  will  be  its  mass,  and,  conse- 
quently, the  longer  the  time  required  by 
it  to  attain  its  full  temperature  elevation. 


84  ELECTRIC   HEATING. 

In  the  case  of  buried  wires,  the  heat 
has  to  be  propagated  slowly  outward 
from  the  wire  through  the  mass  of  the 
neighboring  earth.  The  result  is  that, 
while  the  layers  of  earth  closely  surround- 
ing the  wire  will  probably  reach  95  per 
cent,  of  their  maximum  temperature  ele- 
vation in  half  an  hour,  the  layers  situated 
at  a  considerable  distance  from  the  wire, 
although  they  will  necessarily  receive  a 
much  smaller  temperature  elevation,  yet 
will  require  a  much  longer  time  for  that 
temperature  elevation  to  be  established, 
and  many  hours  may  elapse  before  50  per 
cent,  of  the  maximum  temperature  eleva- 
tion is  attained  at  a  distance .  of  say  four 
feet  from  a  deeply  buried  wire. 

The  temperature  elevation,  which  may 
be  permitted  in  a  wire  buried  in  the 
ground,  is  determined  by  totally  different 


HEATING   OF   COVERED   CONDUCTOKS.      85 

conditions  to  those  which  limit  the  tem- 
perature elevation  of  a  wire  placed  in  a 
building;  for  it  is  evident  that  there  is  no 
danger  of  setting  fire  to  the  ground.  The 
insulating  material  of  a  wire  has,  how- 
ever, to  be  sufficiently  plastic  to  allow  the 
wire  to  be  bent  or  slightly  stretched,  and 
this  condition,  together  with  good  electric 
insulation,  is  usually  found  in  a  substance 
that  will  not  permit  of  a  high  temperature 
without  injury.  Even  if  it  were  possible 
to  operate  a  buried  conductor  at  a  high 
temperature,  such  temperature  would  be 
dangerous  where  the  conductor  emerged 
from  the  ground.  The  temperature  ele- 
vation, in  the  case  of  hemp-covered  wires, 
is  usually  25°  C.  and  in  rubber- covered 
wires  20°  C.  Most  insulating  materials, 
long  before  they  would  be  injured  by  the 
heat,  would  be  liable  to  soften,  thus  per- 
mitting the  conductor  to  sag,  so  that  it 


86  ELECTKIC   HEATING. 

would  no  longer  remain  embedded  central- 
ly in  the  insulating  material.  Conse- 
quently, the  permissible  temperature  el- 
evation is  limited  by  the  softening  point. 

As  regards  the  temperature  elevation  of 
ocean  cables,  employed  in  submarine 
telegraphy,  the  question  is  at  present  de- 
void of  practical  interest,  since  the  cur- 
rents which  such  cables  carry  are  so  very 
feeble,  say  generally  only  a  few  milli- am- 
peres, that  the  temperature  elevation  of 
the  conductor  is  entirely  negligible.  It  is 
worth  pointing  out,  however,  as  an  inter- 
esting fact,  that  should  occasion  ever  arise 
for  sending  powerful  currents  through 
submarine  cables,  the  fact  that  the  entire 
bed  of  the  deep  ocean  is  covered  by  a 
layer  of  very  cold  water  in  the  neighbor- 
hood of  30°  F.,  would  permit  a  ready 
loss  of  heat. 


CHAPTER  V. 

FUSE  WIRES. 

A  WIRE  placed  in  a  building,  although  so 
proportioned  relatively  to  the  current 
strength  it  has  to  carry,  that,  under  ordi- 
nary circumstances  its  temperature  will 
be  perfectly  safe,  yet,  owing  to  acci- 
dental external  causes,  the  current 
strength  may  sometimes  become  enor- 
mously increased,  thereby  heating  the 
wire  to  a  dangerously  high  temperature. 
If,  for  example,  the  wire  has  in  its  cir- 
cuit a  group  of  lamps,  requiring  normally 
10  amperes  of  current  from  a  pressure  of 
115  volts,  then,  if  by  some  accident  a  short- 
circuit  be  effected  at  the  lamps,  the  cur- 
rent strength  through  the  lamps  would 
be  much  diminished,  but  the  strength  of 


S«  ELECTRIC   HEATING. 

current  in  the  wire,  supplying  the  lamps, 
might  become  enormously  increased;  for, 
while  the  pressure  on  the  mains  would 
remain  practically  the  same,  the  resist- 
ance in  the  circuit,  if  very  small,  would 
permit,  by  Ohm's  law,  a  very  powerful 
current  to  pass  through  it. 

The  effect  of  such  an  abnormally  great 
current  would  be  to  cause  the  amount  of 
heat  liberated  in  the  wire,  forming  the 
short  circuit,  to  be  far  greater  than  it 
could  dissipate  without  attaining  a  temper- 
ature sufficiently  high  to  make  it  red  hot, 
or  even  to  melt  it.  If  such  a  wire  were 
melted  by  an  accidental  short-circuit,  not 
only  would  there  be  danger  of  setting  fire 
to  the  wood -work,  or  other  inflammable 
material  surrounding  the  wire,  but  there 
might  also  be  considerable  trouble  and 
difficulty  in  replacing  the  wire  after  the 
accident.  Moreover,  the  effect  of  a  vio- 


DIESEL 

Of) 

FUSE   WIR^S         PRCPEfft"V    f  C 

lent  overload,  sometimeMpiently  great 


to  melt  even  a  stout  cono&r<  forming 
some  portion  of  the  circuiCVould  be 
liable  to  injure  the  dynamo  or  engine 
driving  it,  or  to  overheat  and  consequent- 
ly injure  any  electrical  apparatus  that 
might  be  in  the  same  circuit.  In  order  to 
avoid  these  difficulties  the  plan  has  been 
universally  adopted  of  inserting  wires, 
called  fuse  wires,  in  the  branch  and  main 
circuits  of  any  system  supplied  by  a 
dynamo. 

A  fuse  wire  is  a  wire  or  a  strip  of  metal, 
which  has  both  a  high  electric  resistance 
per  unit  of  length,  and  a  low  melting 
point.  If  such  a  wire  be  in  circuit  with 
a  copper  wire,  and  both  are  of  such  sizes 
that  they  are  able  to  carry  the  normal, 
full-load  current  without  overheating,  it 
will  be  evident  that  the  fuse  wire  must 
become  much  hotter  than  the  copper  wire; 


90  ELECTRIC   HEATING. 

for,  since,  as  we  have  seen,  the  amount  of 
heat  developed  in  any  circuit,  the  current 
strength  remaining  the  same,  depends  on 
the  resistance  of  the  circuit,  it  is  evident 
that  the  same  quantity  of  heat  will  be  de- 
veloped in  such  lengths  of  the  fuse  wire 
and  the  copper  wire,  as  have  an  equal 
drop;  i.  e. ,  offer  an  equal  resistance  to  the 
current.  Consequently,  there  will  be  de- 
veloped in,  say  one  inch  of  fuse  wire,  the 
same  amount  of  heat  as  would  be  liber- 
ated in,  pei haps,  ten  feet  of  copper  wire. 
The  fuse  wire  will,  therefore,  be  raised  to 
the  temperature  at  which  it  melts,  long 
before  the  temperature  of  the  copper  wire 
would  pass  the  danger  point,  and  the 
melting  of  the  fuse  wire  would  interrupt 
the  circuit  and  thus  automatically  cut  off 
the  current.  The  meaning  of  the  term 
safety  fuse  is,  therefore,  evident,  since  the 
simple  introduction  of  such  a  wire  into  the 


FUSE  WIKES.  91 

circuit  would  absolutely  prevent  the  pas- 
sage through  such  circuit  of  a  current 
that  would  raise  its  temperature  to  a  dan- 
gerously high  degree.  It  is  fortunate 
that  so  simple  a  plan  as  the  mere  inser- 
tion of  a  safety  fuse  should  be  capable  of 
protecting  electric  conductors  against  the 
consequences  of  accidental  short  circuits. 
Like  many  other  inventions,  its  value  lies 
largely  in  its  extreme  simplicity,  and  in 
the  certainty  with  which  it  can  be  relied 
upon  to  operate  effectively. 

Fuse  wires  are  composed  of  lead  and 
tin,  or  tin-lead  alloy.  These  wires  usu- 
ally occur  in  the  sizes  shown  in  Fig.  4. 
Here,  on  the  right  hand,  the  diameters  of 
the  wires  are  given  in  circular  mils,  and 
on  the  lefc  hand,  the  carrying  capacity  of 
the  wires  in  amperes.  It  is  to  be  ob- 
served, that  although  the  cross -section  of 


ELECTRIC   HEATING. 


a  wire  is  quadrupled  when  its  diameter  is 
doubled,  yet  the  carrying  capacity  is  not 


CARRYING  CAPACITY 
AMPERES 


FUSE  WIRES 


DIAMETERS 
MILS 

-  20 


31 
36 

50 
70 


32 

42 

56 

68 

78 

83 

96> 

TH 

130 

150 


FIG.  4.— DIAMETER    AND    CARRYING   CAPACITIES   OF  FUSE 
WIRES. 

quadrupled.  The  carrying  capacity  in- 
creases faster  than  the  diameter  of  the 
wire,  but  less  rapidly  than  its  area  of 
cross -section. 


FUSE   WIKES.  93 

Safety  fuses  are  not  only  employed  in 
the  form  of  wires,  but  also  in  the  form  of 
strips,  as  shown  in  Figs.  5  and  6.  In 
Fig.  5,  the  safety  strips  are  connected  to 
the  circuit  by  means  of  binding  posts,  the 
studs  of  which  pass  through  holes  at  each 


FIG.  5.— FUSE  STRIPS. 

end.  In  Fig.  6,  the  ends  of  the  strips  are 
slipped  beneath  the  screw  clamps,  thus 
avoiding  the  necessity  for  the  removal  of 
the  screw  head,  as  would  be  the  case  in 
the  form  shown  in  Fig.  5. 

Fuse  wires,  such  as    shown  in  Fig.  4, 


94  ELECTRIC   HEATING. 

are  placed  in  the  circuit  by  simply  wrap- 
ping them  around  binding  posts  connected 
with  the  circuit  and  firmly  clamping  the 
connection  with  a  screw  head.  This  pres- 
sure is  apt  to  damage  the  wire  and  alter 


FIG.  6.— FUSE  LINKS. 

its  carrying  capacity,  thus  causing  it  to 
melt  at  a  unduly  low  strength  of  current. 
To  avoid  this,  the  ends  of  the  wire  or 


FUSE  WIKES. 


95 


FIG.?.— COPPER-TIPPED  FUSE  WIRES. 

strip  are  often  fused  into  copper  clamps 
as  shown  in  Figs.  7  and  8.  Large  safety 
strips  are  usually  of  the  form  shown  in 
Fig.  8,  the  lead  strip  being  riveted  to  the 
copper  end  pieces. 


FIG.  8.— COPPER-TIPPED  SAFETY  FUSES. 


96  ELECTEIC  HEATING. 

Fig.  9  shows  a  simple  form  of  safety 
fuse-block  consisting  of  a  slab  of  slate,  or 
other  non-inflammable  material,  on  which 
are  mounted  two  metal  blocks  B  and  B. 
The  circuit  passes  through  these  metallic 
blocks,  and  the  fuse  wire  is  clamped  be- 
tween them  as  shown. 


FIG.  9.— SAFETY  FUSE-BLOCK. 

Fig.  10  shows  a  pair  of  strip  safety 
fuses  S19  $2 ,  or  safety  links,  as  they  are 
sometimes  called,  inserted  in  the  circuit 
of  the  two  leads  BB1  and  AA1 ,  under 
thumb  screw  clamps  situated,  at  the  ends 
of  the  metallic  blocks  whiph  form  the 
terminals  of  the  leads  B^  and  A  A1 . 
These  blocks  are  mounted  on  a  non-con- 


FUSE  WIRES.  97 

ducting  and  non-inflammable  plate,  such 
as  a  slab  of  slate,  porcelain,  or  marble. 

Fig.  11  represents  a  porcelain  fuse-block 
prepared  for  the  reception  of  safety 
links  between  the  screw  clamps  A,  A1. 


FiG.lO.—  PAIR  OF  SAFETY  STRIPS,  MOUNTED  ON  FUSE  BLOCK. 

and  B,  Bl .  The  two  supply  mains  A  and 
B  are  electrically  separated  from  each 
other  by  the  porcelain  projecting  ridge 
RR,  provided  for  this  purpose.  The  pres- 
sure between  these  leads  may  be  100  or 
200  volts,  according  to  circumstances,  and 


98 


ELECTKIC   HEATING. 


were  the  ridge  not  present,  the  blowing 
of  the  fuse  might  establish  a  dangerous 


FIG.  11.— PORCELAIN  FUSE-BOX. 

arc  across  the  leads,  or  such  arc  might  be 
accidentally  established  during  the  proc- 


FUSE  WIKES.  99 

ess  of  connecting  the  safety    links   and 
thus,  perhaps,  injure  the  attendant. 

Fuse-boxes  are  generally  provided  with 
a  porcelain  cover,  though  at  times,  for  the 
purpose  of  ready  inspection,  a  transpar- 
ent cover,  such  as  glass  or  transparent 
mica,  is  employed.  Figs.  12  and  13  show 
examples  of  fuse-blocks  of  the  latter  type 
with  the  fuse  wires  or  links  in  position. 
The  arrangement  of  the  box  will  neces- 
sarily vary  according  to  whether  the  main 
wires  terminate  in  the  box,  or  pass 
through  it.  Thus  at  A,  Fig.  12  ,  the  mains 
pass  directly  through  the  box  in  the 
grooves  on  the  left  hand,  but  after  being 
bared  of  their  insulation,  have  their  con- 
ductors clamped  underneath  the  screws 
whose  heads  are  visible  in  the  grooves. 
Connections  exist  beneath  the  box  from 
these  screws  to  the  safety  links  on  the 
right-hand  side  and  the  branch  wires  are 


100 


ELECTRIC  HEATING. 


B 


FIG.  12.—  MICA-COVERED  FUSE-BOXES. 

carried  off  at  right  angles.  In  the  event 
of  any  short-circuit  between  the  branch 
wires,  one  or  both  of  the  safety  links  is 


FUSE   WIRES.  101 

melted,  but  no  accident  in  the  main  cir- 
cuit can  affect  these  fuses,  since  the  main 


FIG.  13.— MICA-COVERED  FUSE-BOXES. 

conductors,   as  already  mentioned,  pass 
directly  through  the  box. 


102  ELECTRIC  HEATING. 

At  B,  is  shown  a  form  of  safety  fuse-box 
through  which  the  mains  do  not  pass,  but 
terminate,  say  at  the  left,  and  the  wires 
supplied  by  such  mains  enter  at  the  right. 

At  (7,  a  form  is  shown  from  which  two 
separate  branch  circuits  issue  from  the 


FIG.  14.  —FUSE- Box  PROVIDED  WITH  PORCELAIN  COVER. 

box,  half  to  the  right  and  half  to  the  left, 
after  being  suitably  connected  to  the 
mains  which  enter  and  pass  through  the 
centre  of  the  box. 

Practically  similar  forms  are  shown  in 
Fig.  13, 


FUSE   WIRES. 


103 


FIG.  15.— FUSE-BOX  WITH  FUSES  IN  COVER. 


104 


ELECTRIC  HEATING. 


In  all  these  forms,  a  thin  mica  cover 
serves  to  exclude  dust,  and,  at  the  same 
time,  renders  the  conditions  of  the  safety 
links  externally  visible. 

Figs.  14  and  15  show  forms  of  fuse- 
boxes,  provided  with  porcelain  covers. 


FIG.  16.— CEILING-FIXTURE  FUSE-BLOCK. 

The  form  shown  in  Fig.  14  is  similar  to  the 
box  shown  in  Fig.  11,  with  the  addition  of 
sides  and  cover.  Fig.  15  shows  a  form 
of  box  in  which  the  safety  links  are  sup- 
ported on  the  cover,  and  the  wires  con- 


FUSE   WIKES. 


105 


nected  to  the  base,  so  that  the  attach- 
ment of  the  cover  to  the  base  closes  the 
circuit  through  the  links. 

The  form  of  fuse-box  necessarily  varies 
with  the  current  which  has  to  be  carried 
through  it,  and  with  the  character  of  the 


FIG.  17.— CEILING  BLOCK  WITH  SPRING  CLIPS. 

fixture  or  circuit  in  which  it  is  connected. 
Fig.  16  shows  a  form  suitable  for  a  ceil- 
ing fixture;  i.  e.,  an  electrolier  pendant 
from  a  ceiling  and  usually  called  a  ceiling 
block.  The  supply  wires  are  connected  to 
the  screws  S,  S,  in  the  permanent  block 


106  ELECTKIC   HEATING. 

which  is  attached  to  the  ceiling,  while  the 
wires  connected  to  the  electrolier  are  con- 
nected to  the  screws  B,  B,  in  the  cover. 
Connection  is  secured  through  the  two 
safety  fuses  F,  F,  by  screwing  up  the 
cover  against  the  block.  A  similar  form 
is  shown  in  Fig.  17,  in  which,  however, 
connection  is  secured  through  spring 
clips. 


FIG.  18.— PLUG  CUT-OUT. 

The  fuse  wire  is  sometimes  placed  in  a 
screw-socket  in  order  to  ensure  ease  in 
placing  and  replacing.  Under  these  cir- 
cumstances the  electrical  connections  of 
the  fuse  wire  are  such  that  the  mere  in- 
sertion of  the  screw  block  in  its  socket 


$ir£uit.    Fig.  18, 


inserts  the  fuse  in 

shows  such  a  screw - 

out  and  Fig.   19  shows  various  forms  of 

socket    attachments,   or  cut-out  boxes,  for 

such    fuses.     The  cavities  of  the  block 

containing  the  fuse  wires  are  usually  part- 


PIG.  19.— CUT-OUT  BOXES. 

ly  filled  with  plaster -of -Paris  for  the  pur- 
pose of  excluding  the  air;  for,  when  a  fuse 
wire  suddenly  melts  or  blows,  the  heated 
air  might  escape  explosively  from  the 
cavity  forcing  particles  of  melted  lead 
outward.  The  effect  of  the  plaster-of- 


108  ELECTEIC  HEATING. 

Paris  on  the  action  of  the  fuse,  is  to  di- 
minish its  sensitiveness  to  a  momentary 
overload,  for  the  plaster  conducts  heat 
from  the  wire,  and,  therefore,  a  sudden 
excess  of  heat  will  not  so  quickly  bring 
the  wire  to  the  melting  point,  although  a 
steadily  continued  current  will  eventual- 
ly melt  the  fuse  almost  as  readily  as  if 
the  plaster  were  absent. 

When  fuse -blocks  are  placed  inside  ap- 
paratus, it  becomes  a  matter  of  impor- 
tance to  insure  convenience  in  inserting 
and  inspecting  them,  and  when  such  ap- 
paratus, as,  for  example,  an  alternating- 
current  transformer,  employs  dangerous- 
ly high  pressures,  some  means  are  neces- 
sary in  order  to  insure '  safety  of  attach- 
ing the  fuse  wires  to  the  fuse -block  by 
disconnecting  them  from  the  primary  and 
secondary  terminals.  A  form  of  such  a 


FUSE  WIEES.  109 

fuse-block  is  shown  in  Fig.  20.    Here  an 
iron  box   BB,  encloses  a  porcelain  fuse- 


FIG.  20.— TRANSFORMER  SAFETY  FUSE-BOX 

box,  whose  cover  (7,  is  removed  to  show 
the  interior.     In  this  case,  the  porcelain 


110  ELECTHIC  HEATING. 

fuse-blocks  are  detachable.  One  of  them 
is  shown  at  F,  detached,  and  the  other  at 
F\  in  place  of  the  interior.  The  fuse  wire 
w,w,  is  clamped  under  screws  whose 
studs  project  through  the  fuse-block  and 
enter  into  spring  clips  p,  p\  when  the  fuse- 
block  is  thrown  into  position  by  its  han- 
dle 7i,  is  connected  with  the  external 
circuit  by  a  wire  shown,  and  P\  connected 
to  the  apparatus  in  the  interior.  Should 
any  short  circuit  exist  in  the  apparatus, 
the  fuse  will  melt  on  the  insertion  of  the 
block,  and  the  hand  of  the  operator  will 
be  protected  from  any  particles  of  explod- 
ed lead  by  reason  of  the  shielding  action 
of  the  handle  h. 

The  temperature  at  which  a  fuse  wire 
will  melt,  depends  upon  its  composition. 
Some  alloys  can  be  used  which  will  melt 
at  as  low  a  temperature  as  50°  C.  As  a 


FUSE  WIRES.  Ill 

rule,  however,  the  melting  point  is  about 
300°  C. 

The  current  strength  which  will  melt  a 
fuse  depends  upon  a  variety  of  circum- 
stances. It  might  be  supposed  that  for  a 
given  diameter  of  fuse  wire,  the  length 
of  the  wire  forming  the  fuse  would  not 
influence  its  melting  point.  Such,  how- 
ever, is  not  the  case.  A  long  fuse  wire 
will  usually  melt  at  a  lower  current 
strength  than  a  short  fuse  wire,  principal- 
ly for  the  reason  that  the  heat  generated 
in  a  short  wire  is  conducted  by  the  metal 
in  the  wire  to  the  metallic  masses  form- 
ing the  clamps  at  each  end,  thus  enabling 
the  heat  in  the  wire  to  be  dissipated  more 
rapidly  than  would  be  possible  in  the  case 
of  a  longer  fuse.  Similarly,  the  position 
of  a  fuse  wire,  whether  closely  surrounded 
in  a  practically  air-tight  chamber  or  free- 
ly exposed  to  such  currents  of  air  as  might 


112  ELECTKIC   HEATING. 

exist  in  its  vicinity,  would  greatly  effect 
the  current  strength  that  melts  it.  So 
also  the  position  of  the  wire,  whether  ver- 
tical or  horizontal,  its  shape,  whether 
straight  or  curved,  the  shape  of  its  cross - 
section,  the  character  of  its  surface, 
whether  rough  or  smooth,  tarnished  or 
bright,  all  exert  an  influence  on  its  carry- 
ing capacity.  As  a  rule,  therefore,  fuses 
cannot  be  depended  upon  to  melt  at  pre- 
cisely the  current  strength  for  which  they 
are  designed. 

When  an  overload,  or  an  unduly  power- 
ful current,  exists  in  an  electric  circuit 
for  a  very  brief  interval  of  time,  as,  for 
example,  when  a  short  circuit  occurs  dur- 
ing a  small  fraction  of  a  second,  a  fuse  de- 
signed to  melt  at  say,  10  amperes,  may 
carry  100  amperes  or  more  without  melt- 
ing, when  10  amperes  steadily  maintained 


FUSE  WIKES.  113 


for  one  minute  would  insure  the  melting 
of  the  fuse.  This  is  for  the  reason  that 
heat  has  to  be  expended  in  the  mass  of 
the  fuse  before  its  temperature  can  be 
raised  to  the  melting  point.  Consequent- 
ly, an  appreciable  fraction  of  a  second 
may  be  required  for  even  a  powerful  cur- 
rent to  develop  this  heat;  while,  when  10 
amperes  flow  steadily  through  it,  ample 
time  is  afforded  to  bring  up  the  tempera- 
ture of  the  metal. 

It  sometimes  occasions  surprise  that 
when  a  dynamo  supplies  a  distant  branch 
circuit  through  two  fuses,  one  of  which,  a 
large  fuse  near  the  dynamo,  called  the 
main  circuit  fuse,  is  capable  of  carrying, 
say  500  amperes,  and  the  other,  a  small 
branch  fuse  in  a  branch  circuit,  is  capable 
of  carrying  only  20  amperes,  that  on  an 
accidental  short-circuit  in  the  branch  cir- 


114  ELECTRIC   HEATING. 

cuit,  the  main  fuse  should  blow  out,  while 
the  branch  fuse  remains  intact.  1  his  ac- 
tion, by  no  means  of  common  occurrence, 
probably  finds  its  explanation  in  the 
fact  that  the  main  fuse  has  already  been 
heated  by  a  full-load  current  of  the  gener- 
ator, to  a  comparatively  high  temperature, 
while  the  particular  branch  fuse  is  cold 
since  no  current  had  been  passing  through 
it  prior  to  the  accidental  short  circuit. 
Under  these  circumstances,  when  a  short- 
circuit  suddenly  occurs  between  the 
branch  wires,  the  powerful  rush  of  cur- 
rent through  both  fuses  may  be  able  to 
blow  the  larger  fuse,  before  the  smaller 
one  reaches  the  temperature  of  its  melt- 
ing point. 

Since  in  most  commercial  electric  cir- 
cuits fairly  considerable  variations  in  the 
strength  of  the  current  passing  are  apt  to 


FUSE   WIRES.  115 

exist  without  constituting  either  a  dan- 
gerous or  objectionable  overload,  if  the 
carrying  capacity  of  the  fuses  is  made  too 
near  their  normal-load  current,  consider- 
able inconvenience  may  arise  from  the 
frequency  with  wThich  the  fuses  are  blo\vn. 
For  this  reason,  in  good  practice,  fuses 
are  generally  employed  whose  carrying 
capacity  is  about  fifty  per  cent,  greater 
than  the  full-load  current. 

In  central  stations  supplying  under- 
ground systems  of  conducting  mains,  the 
inconvenience  above  pointed  out  arising 
from  the  blowing  of  fuses  is  so  marked 
that  in  many  cases  such  fuses  are  omitted 
entirely  in  the  central  station,  and  are 
only  inserted  between  the  mains  and  the 
consumers,  as  well  as  in  all  the  branch 
circuits  of  the  house  wirings.  Should,  for 
example,  a  large  feeder  either  become 


116  ELECTRIC   HEATING. 

overloaded,  or  develop  a  short  circuit  at 
some  point  underground,  it  would  prob- 
ably blow  its  fuse,  and  the  extra  load 
would,  therefore,  be  transferred  to  other 
feeders.  These  in  their  turn  would  also 
be  liable  to  blow  their  fuses,  until,  in 
some  cases,  the  entire  system  of  feeders 
and  mains  might  thus  be  cut  off  from  the 
dynamos. 


CHAPTER  VI. 

ELECTRIC  HEATERS. 

ONE  of  the  commercial  uses  to  which 
electricity  has  lately  been  applied  has 
been  the  artificial  heating  of  air  in  build- 
ings on  a  comparatively  small  scale. 
While  this  method  of  obtaining  artificial 
warmth  has  not  yet  reached  such  economy 
as  to  permit  it  to  be  economically  applied 
to  the  heating  of  the  air  of  large  buildings, 
yet  the  convenience  arising  from  the  facil- 
ity with  which  the  electric  current  can  be 
led  to  the  electric  heater,  the  comparative- 
ly small  size  and  portability  of  the  latter, 
the  readiness  with  which  the  current  can 
be  turned  on  and  off,  the  safety  of  the  ap- 
paratus, its  freedom  from  fumes  or  dirt, 
and  the  ease  with  which  it  can  be  managed, 


118  ELECTRIC   HEATING. 

have  attracted  no  little  attention,  and  its 
use,  in  "certain  directions,  is  rapidly  in- 
creasing. While  there  is,  perhaps,  little 
probability  in  the  near  future  of  large 
electric  plants  being  erected  whose  cur- 
rent shall  be  entirely  employed  for  the 
production  of  heat,  as  in  warming  build- 
ings, nevertheless,  electric  heaters  are 
likely  to  be  extensively  employed  in  con« 
nection  with  already  existing  systems  of 
electric  distribution  for  light  and  power. 

Electric  heaters  are  to-day  in  common 
use  in  electric  street  railway  cars,  and 
this  is  for  the  same  reason  that  electric 
lights  are  employed  in  these  cars.  Were 
it  not  for  the  fact  that  the  cars  obtain  their 
propelling  power  from  the  electric  cur- 
rent, it  is  not  at  all  likely  that  electrically 
lighted  and  electrically  heated  cars  would 
have  come  into  the  general  use  they  have 


ELECTKIC    HEATERS.  119 

to-day;  although  in  parlor  cars  on  steam 
railroads,  electric  incandescent  lamps  are 
sometimes  employed  as  luxuries. 

Electric  heaters,  designed  for  the  artifi- 
cial warming  of  air,  though  made  in  a  great 
variety  of  forms,  consist  essentially  of  a 
metallic  conducting  wire,  generally  of 
galvanized  iron,  or  German  silver,  loosely 
coiled  so  as  to  possess  a  comparatively 
extended  radiating  surface,  and  common- 
ly supported  in  the  air. 

In  order  to  obtain  a  sufficiently  extend- 
ed surface  for  radiation  and  convection, 
and  also  to  obtain  the  desired  electric 
resistance  in  the  coil,  within  a  limited 
space,  it  is  usual  to  wind  the  wire  in  a 
loose  spiral  around  a  form  or  block  of 
earthenware,  porcelain,  or  other  similar, 
non-inflammable  material. 

We  have  seen  that  a  definite  relation 


120  ELECTKIC   HEATING. 

exists  between  a  given  amount  of  electric 
energy  and  the  heat  energy  it  is  capable 
of  producing.  It  has  been  ascertained 
that  one  joule  of  work,  expended  in  pro- 
ducing heat,  will  raise  the  temperature  of 
a  cubic  foot  of  air  about  TV°F.,  and, 
therefore,  an  activity  of  one  joule-per- 
second,  or  one  watt,  can  raise  the  tem- 
perature of  one  cubic  foot  of  air  TV  °  F. 
per  second. 

A  simple  form  of  cylindrical  electric 
heater  for  hot  air  is  shown  in  Fig.  21.  It 
consists  of  a  metallic  strip,  wound  spiral- 
ly on  an  insulated  frame.  Here,  as  in  all 
forms  of  air  heater,  the  design  is  to  obtain 
as  large  a  surface  exposed  to  the  air  as 
possible.  Since  the  metal  strip  employed 
is  comparatively  thin,  the  total  mass  or 
weight  of  the  metal  in  the  heater  is  com- 
paratively small,  and  the  conductor  is 
rapidly  heated  by  the  passage  of  the  cur- 


ELECTRIC  HEX£§5^. 

N^fc* 


PROPERTY  CF  '2 

^ 
121 


PIG.  3L— CYLINDRICAL  ELECTRIC  HEATER. 


122  ELECTEIC   HEATING. 

rent.  But  since  the  surface  exposed  to 
the  air  is  great,  the  heating  coil  never  ac- 
quires an  excessively  high  temperature. 
An  electric  heating  coil  best  serves  its 
purpose  when  it  rapidly  imparts  its  heat 
to  the  surrounding  air,  never  itself  acquir- 
ing a  dangerously  high  temperature. 

The  heating  coil  or  conductor  in  an  elec- 
tric heater  is  not  always  in  the  form  of 
a  strip.  It  sometimes  takes  the  form  of 
a  wire  or  spiral,  either  bare,  or  placed 
within  a  metallic  frame. 

Fig.  22  represents  a  form  of  electric 
heater  or  radiator  resembling  in  appear- 
ance an  ordinary  steam  or  hot  water  ra- 
diator. Here  the  coils  of  the  electric  con- 
ductor are  placed  within  the  metallic 
frame.  The  exact  length  and  dimensions 
of  the  heater  coils  will  depend  upon  the 
amount  of  heat  required,  and  on  the  elec- 


ELECTRIC  HEATERS. 


123 


trie  pressure  employed  in  the  building. 
The  same  coil  will,  however,  give  practi- 
cally the  same  amount  of  heat  when  con- 


FIG.  22.— ELECTRIC  RADIATOR. 

nected  with  the  same  pressure  of  either 
alternating  or  continuous  current. 

The  advantages  of  an  electric  heater 
are  especially  marked  when  employed  in 
cars  propelled  by  electricity.  Indeed, 


124  ELECTRIC   HEATING:. 

the  necessity  for  utilizing  all  the  available 
space  in  a  street  car  for  the  accommoda- 
tion of  passengers,  and  for  maintaining  a 
uniform  temperature,  with  a  minimum  of 
attention  required  from  the  conductor  of 
the  car,  renders  the  use  of  the  electric  cur- 
rent for  heating  even  more  economical 
than  the  use  of  a  stove.  This,  of  course, 
arises  largely  from  the  fact  that  the  stove 
which  can,  in  practice,  be  placed  in  the 
limited  space  allotted  to  it  in  a  car,  must 
necessarily  be  very  uneconomical ,  more- 
over, the  large  scale  on  which  electric 
power  is  generated  in  a  central  station  for 
propelling  the  cars,  reduces  the  cost  of 
the  electric  energy  so  much  that  the  elec- 
tric heating  of  the  car  actually  compares 
very  favorably  in  economy  with  what 
would  be  required  to  heat  it  as  effectively 
by  the  direct  burning  of  coal  in  a  stove. 
Fig.  23  represents  a  form  of  electric  cwr 


ELECTRIC   HEATERS. 


125 


heater,  in  front  elevation,  and  Fig.  24,  the 
back  and  interior  of  the  same  heater, 
showing  the  electric  coil  in  position.  Four 
or  six  of  these  heaters  are  employed  in 
each  car,  according  to  the  size  of  the  car 
and  the  climate  of  the  locality  in  which  it 


FIG.  23.— ELECTRIC  CAR-HEATER. 

rnns.  The  heater  is  placed  in  a  hole  or  gap 
made  in  the  riser,  or  vertical  partition,  be- 
low the  car  seat.  A  cast-iron  plate,  fur- 
nished with  grid  openings,  placed  in  the 
front  of  the  heater  and  opening  into  the 
car,  serves  the  double  purpose  of  prevent- 


126  ELECTRIC   HEATING. 

ing  the  dress  of  the  passengers  from  com- 
ing into  contact  with  the  heated  coils, 
and  for  permitting  the  ready  escape  of 
the  air  through  the  apparatus. 

An  inspection  of  Fig.  24  will  show  that 
the  heating  coil,  employed  in  this  particu- 
lar form  of  car  heater,  consists  of  a  close 


Fia.  24.— BACK  AND  INTERIOR  OF  ELECTRIC  CAR- HEATER. 

spiral  conductor,  which  is  spirally  wound 
around  a  grooved  porcelain  tube,  and  is 
supported  at  the  centre  and  at  the  two 
ends  by  porcelain  washers.  The  back 
of  the  heater  is  formed  of  sheet  iron, 
suitably  provided  with  asbestos  lining. 


ELECTRIC   HEATERS. 


127 


Heaters  employed  on  electric  railroad 
circuits  take  their  current  from  the  mains 
at  a  constant  pressure,  generally  500  volts. 
In  order  to  vary  the  current  passing 


FIG.  25.  -CAR-HEATER  REGULATING  SWITCH. 

through  the  four  or  six  heaters  generally 
employed  in  each  car,  a  switch  is  used, 
by  means  of  which  the  separate  heater 


128  ELECTRIC  HEATING. 

coils  can  be  connected  in  series,  or  in 
parallel -series,  or  some  of  them  cut  out 
from  the  circuit,  thus  permitting  the 
amount  of  heat  to  be  readily  varied  in  or- 
der to  meet  the  requirements  of  the 


^^^tes™.'-1 

FIG.  26. — SIDE  INTERIOR  VIEW  OF  CAR- HEATER  REGULAT- 
ING SWITCH. 

weather.  Fig.  25  shows  a  form  of  reg- 
ulating switch  of  this  character  intended 
to  produce  five  different  strengths  of 
current,  and,  therefore,  five  different  rates 


ELECTKIC    HEATERS.  129 

of  producing  heat  in  the  car.  The  side 
view  of  the  interior  of  the  switch  is  shown 
in  Fig.  26;  the  front  view  of  the  interior 
of  the  switch  in  Fig.  27.  This  switch 
consists  of  a  number  of  contact  springs, 


•  .  __^ 


FIG.  27.— FRONT  INTERIOR  VIEW  OF  CAR-HEATING  KEGU- 
LATING  SWITCH. 

whereby,  through  the  motion  of  a  lever 
attached  to  the  barrel,  the  proper  connec- 
tions can  be  made  for  coupling  the  coils  in 
the  five  different  arrangements  required. 


130 


ELECTEIC   HEATING. 


The  connections  from  the  switch  to  the 
trolley  wire  and  the  ground  through  the 
various  heaters,  is  shown  in  Fig.  28.  In 
position  No.  1  all  the  coils  are  connected 
in  series,  so  that  the  current  has  to  pass 
through  each  in  succession.  This  position 


AUTOMATIC  CUT  OUT 


• 

{-                                              Zs"*s 

>!=              !pS= 

b^    ^          ,  -p 

TO  GROUND 

|  AAAAAAAAA_AAV\AAAAA/|1                       I  A\AMAAAA_AAAAAV\AA|                        |  AAA,AAAAA\-AAAAAAAA 

^             sf- 

FIG.  28. — DIAGRAM  OP  WIRING  FOR  Six  ELECTRIC  HEATER 
EQUIPMENT. 

corresponds  to  the  minimum  current 
strength,  about  2  amperes,  and,  therefore, 
to  the  minimum  thermal  activity,  or  rate 
of  developing  heat;  namely,  about  one 
kilowatt.  In  position  2,  two  heaters  are 


ELECTEIC    HEATERS.  131 

entirely  cut  out  of  the  circuit,  so  that  the 
resistance  of  the  series  being  diminished, 
the  current  strength  and  activity  in  the 
lemainder  are  increased,  and  the  four  ac- 
tive heaters  will  supply  more  heat  to  the 
car  than  the  six  heaters  in  the  first  case, 
the  current  being  nearly  3  amperes,  and 
the  activity  nearly  1500  watts.  In  the 
third  position,  the  six  heaters  are  con- 
nected in  two  series  of  3  each,  so  that  the 
current  strength  in  each  series  is  about 
twice  that  in  the  first  position,  or  about 
3J  amperes  in  each  series;  /.  e.t  7  amperes 
or  3.5  KW.  in  the  combination.  The 
fourth  position  connects  two  sets  of  two 
heaters  and  cuts  out  two  heaters  entire- 
ly. This  gives  about  4  amperes  in  each 
series,  or  8  in  the  combination,  represent- 
ing 4  KW.  In  the  fifth  position,  three 
rows  of  two  heaters  are  employed,  the 
current  in  each  row  being  4  amperes,  or 


132 


ELECTKIC   HEATING. 


FIG.  29.— CAB-HEATER. 


ELECTRIC    HEATEES.  133 

12  amperes  in  all,  and  the  activity  about 
6  KW. 

Another  form  of  car-heater  is  shown  in 
Fig.  29.  Here  the  heating  coil  shown  at 
A,  consists  of  a  wire  wrapped  in  one  long 
spiral  around  the  insulated  grid  or  frame. 
The  heating  coil  is  enclosed  in  a  perfor- 
ated iron  cover  shown  at  B,  while  at  C, 

"I 
£^3^m*  , 


FIG.  30. — PORTABLE  AIR  HEATER, 

the  coil  with  its  cover  is  shown  in  posi- 
tion below  the  car  seat.  Here  the  air 
enters  the  heater  from  the  lower  aper- 
tures and  issues  from  those  above, 
after  passing  over  the  heated  wires. 


134 


ELECTRIC    HEATING. 


Portable  electric  heaters,  as  their  name 
indicates,  are  so  constructed  that  they 
may  be  readily  carried  and  temporarily 
attached  in  any  room  where  electric  sup- 
ply is  obtainable.  These  are  made  in  a 


FIG.  31.— PORTABLE  ELECTRIC  HEATER. 

variety  of  forms,  but  the  principle  in  all 
cases  is  the  same,  A  wire  of  suitable 
length  and  size  is  enclosed  in  the  heater 
and  free  access  given  to  it  from  the 
surrounding  air.  A  form  of  cylindrical 
heater  is  represented  in  Fig.  30.  Other 


ELECTRIC    HEATERS. 


135 


forms  of  portable  heaters  are  shown  in 
Figs.  31,  32,  33  and  34.  That  shown  in 
Fig.  33  is  26  in.  long,  7  in.  in  height,  and 
lOJ  in.  wide,  and  is  provided  with  three 
switches  to  regulate  the  temperature.  A 


FIG.  32.— PORTABLE  HEATER. 


flexible  attachment  of  the  conductors  to 
the  heater  is  shown  in  Fig.  34.  Fig.  35 
represents  a  small  stationary  heater  in- 
tended for  attachment  to  a  wall,  corre- 


136  ELECTRIC  HEATING. 

spending,  it  may  be,  in  position,  to  the 
ordinary  hot-air  register. 

Figs.  36  and  37  show  a  form  of  electric 
heater  suitable  for  office  or  house  work. 


FIG.  33.— PORTABLE  HEATER. 

Fig.  36  shows  the  exterior,  and  Fig.  37, 
the  interior  of  the  apparatus.  The  heat- 
ing coils,  six  in  number,  are  essentially  of 
the  same  type  as  those  employed  in  con- 
nection with  the  oar -heaters  represented 


ELECTRIC   HEATERS. 


137 


FIG.  34.— ATMOSPHERIC  HEATER. 


138  ELECTKIC   HEATING. 

lnvFigs.  23  and  24.  The  coils  are  wound  on 
vertical  porcelain  frames,  as  shown  in  Fig. 
37,  and  are  sometimes  provided  with  atem- 
perature- regulating  switch  in  such  a  man- 
ner that  they  may  be  connected  in  series, 
or  parallel -series,  and  so  produce  less  or 
greater  activity.  The  stove  case  shown 
in  Fig.  36,  is  made  of  Russia  iron.  The 
air  enters  at  the  bottom  of  the  heater, 


FIG.  35.— WALL  HEATER. 

passes   up    over  the    heated   wire,   and 
escapes  at  the  top. 

Electric  air  heaters  may  be  employed 
for  a  variety  of  purposes,  as,  for  example, 
for  drying  out  the  interiors  of  large  cais- 
sons or  tanks.  A  form  of  heater  suitable 
for  this  purpose  is  represented  in  Fig.  38. 
It  consists,  as  shown,  of  a  number  of  coils, 


ELECTRIC 


ttfiTVCF  's 


FIG.  36,— PORTABLE  ELECTRIC  HEATER. 


140 


ELECTRIC   HEATING. 


capable  of  being  connected  either  in  series 
or  in  parallel.  It  is  33  in.  long,  12  in.  wide, 


FIG.  37.— PORTABLE  ELECTRIC  HEATER,  INSIDE  VIEW, 

7  in.  in  height,  and  is  intended  for  a  pres- 
sure of  110  volts  with  a  maximum  current 


ELECTRIC  HEATERS. 


141 


strength  of  42  amperes ;  i.  e. ,  a  maximum 
activity  of  4.62  KW. 

As  we  have  already  seen,  the  product 
of  the  drop  of  pressure  in  a  conductor 
and  the  current  strength,  equals  the  ther- 
mal activity  in  the  conductor.  Since  in  a 
heating  coil,  the  drop  is  entirely  of  this 


FIG.  38  —TANK  HEATER. 

nature,  it  is  evident  that  all  the  energy  of 
the  current  passing  through  the  coil  must 
appear  in  the  circuit  as  heat,  and  all  of 
this  heat  energy  must  be  given  to  the  ex- 


142  ELECTRIC  HEATING. 

ternal  air  on  the  cooling  of  the  coil.  Con- 
sequently, neglecting  that  small  portion 
which  is  dissipated  by  conduction  to  the 
walls  or  floor,  an  electric  air  heater,  as  a 
device  for  converting  electric  energy  into 
heat  energy,  may  be  regarded  as  a  nearly 
perfect  machine. 

The  cost  of  operating  a  car -heater  will 
necessarily  vary  with  the  amount  of  ac- 
tivity developed  in  the  car,  and  this,  of 
course,  will  depend  upon  the  number  of 
amperes  passing  through  the  coils  and 
the  manner  in  which  the  coils  are  con- 
nected by  the  regulating  switch.  If,  for 
example,  there  are  four  heaters  in  a  car, 
and  their  resistance  is  62.5  ohms  each, 
then,  when  they  are  connected  in  series, 
the  total  resistance  of  the  heating  circuit 
will  be  say,  250  ohms.  Assuming  the 
pressure  to  be  uniformly  maintained  at 


ELECTRIC   HEATERS.  143 

500  volts,  the  current  strength  will  be  2 
amperes,  and  the  thermal  activity  1000 
watts,  or  1  KW.  If  the  coils  are  connect- 
ed in  two  rows  of  two  each,  the  increased 
current  which  would  flow  through  them 
would  increase  the  resistance  of  each  coil, 
by  increasing  its  temperature,  but  as- 
suming, for  the  sake  of  simplicity,  that 
this  increase  of  resistance  is  negligible, 
then  the  resistance  of  the  coils,  connected 
in  two  rows  of  two,  will  be  62^  ohms,  and 
a  current  of  8  amperes  will  pnss,  making 
the  activity  4000  watts,  or  four  times  as 
great  as  in  the  preceding  case.  It  is, 
of  course,  impossible  to  determine  from 
these  figures  alone  what  the  temperature 
in  the  car  will  be,  since  the  air  is  being 
renewed  by  ventilation,  and  by  the  occa- 
sional opening  of  the  car  door.  Moreover, 
the  temperature  produced  will  vary  with 
the  temperature  of  the  external  air,  the 


144  ELECTRIC   HEATING,. 

speed  of  the  car,  and  with  the  direction 
and  intensity  of  the  wind.  Consequently, 
in  practice,  it  is  necessary  to  provide  for  a 
variable  production  of  heat  so  as  to  meet 
the  requirements  of  a  variable  climate. 
It  is  found  that  the  average  amount  of 
current  required  to  warm  the  car,  except 
in  extremely  cold  climates,  is  three  am- 
peres at  a  pressure  of  500  volts,  or  1| 
kilowatts.  The  cost  of  a  KW.  hour,  when 
supplied  from  a  large  power  station  to  an 
extended  system  of  cars,  is  usually  a  little 
over  one  cent  and  a  half,  per  kilowatt- 
hour  delivered.  At  this  estimate,  the 
average  cost  of  heating  a  car  in  the  winter 
is  about  2. 25  cents  per  hour,  or  40.5  cents 
per  car -day  of  18  hours.  The  cost  is 
stated  to  vary  from  25  cents  to  50  cents 
per  car -day  of  18  hours,  according  to  the 
number  of  cars  and  the  nature  of  the 
weather.  It  has  been  stated,  from  actual 


ELECTRIC   HEATERS.  145 

measurement  in  Boston,  that  cars  having 
two  doors,  12  windows  and  850  cubic  feet 
of  space  can  be  heated  to  an  average  tem- 
perature elevation  of  25L  F.  above  the  ex- 
ternal air  during  severe  wintry  weather 
by  an  expenditure  of  2.5  KW. 

Leaving  out  of  consideration,  however, 
the  cost  of  the  electric  heating  of  a  car, 
the  advantages  this  method  possesses 
over  heating  by  a  coal  or  oil  stove  ai'e  con- 
siderable. A  stove  fails  to  produce  that 
uniform  temperature  so  necessary  to  the 
comfort  of  the  passengers,  the  centre  of 
the  car  being  more  powerfully  heated 
than  the  ends.  The  electric  heater  warms 
the  air  near  the  floor  of  the  car,  where 
warmth  is  most  agreeable.  Moreover, 
the  electric  heater  requires  practically  no 
attention,  does  not  necessitate  the  re- 
moval of  dust,  ashes  or  coal,  and  occupies 


146  ELECTRIC   HEATING. 

no  paying  space.  Consequently,  where 
electric  cars  are  used,  the  electric  heater 
is  coming  into  extended  use,  not  only  on 
account  of  its  greater  popularity,  but  also 
on  account  of  its  convenience. 

When  it  is  desired  to  apply  heat  di- 
reetly  to  the  surface  of  the  body,  for  such 
medical  treatment  as  would  ordinarily 
employ  hot  water  bags,  the  object  can  be 
muc*h  more  conveniently  obtained  by  a 
suitably  constructed  electric  heater  tluin 
by  any  method  which  depends  for  its 
heat  on  material  warmed  while  away 
from  its  body,  since,  in  all  such  cases, 
the  cooling  of  the  material  necessitates  its 
repeated  renewal.  An  electric  heater, 
suitable  for  local  application  to  the  body, 
and  called  a  flexible  electric  heater,  is 
shown  in  Fig.  39,  because  constructed  of 
materials  which  enable  it  to  be  brought 
into  intimate  contact  with  the  surface  to 


ELECTKIC   H 

be    heated.     The 
formed  of  German  silver  wire  arrai 
shown  in  the  figure,  placed  on  asbestos 
cloth  and  suitably  insulated.     The  space 


PIG.  39. -FLEXIBLE  ELECTRIC  HEATER. 

surrounding  the  wires  is  filled  with  a 
solution  of  silicate  of  soda,  which,  on 
hardening,  acts  as  a  cement  to  hold  the 
different  parts  together.  A  cushion,  or 
flexible  mass,  is  then  made  by  packing 


148  ELECTRIC    HEATING. 

mineral  wool,  or  asbestos  fibre,  around  the 
heating  conductor  and  covering  the  mass 
with  a  suitable  cover  of  cloth.  The  ad- 
vantage of  such  a  heater  is  that  the  heat 
can  be  readily  maintained.  The  appara- 
tus shown  in  the  figure,  ordinarily  re- 
quires to  be  supplied  with  an  activity  of 
about  fifty  watts. 

The  electric  heater  has  recently  been 
adopted  for  the  warming  of  the  Vaudeville 
Theatre  in  London,  England.  The  advan- 
tages of  electric  heating  are  specially 
marked  in  the  case  of  theatres,  where 
pure,  warm  air,  without  powerful  current  3 
or  draughts  are  the  desiderata.  The 
heaters  are  two  feet  long  and  one  foot 
wide.  Twelve  of  these  are  attached  to 
the  skirtings  round  the  walls,  and  twelve 
to  the  partition  in  front  of  the  orchestra. 
Four  large  portable  heaters  are  also  em- 
ployed with  flexible  attachments  for  use 


ELECTRIC   HEATERS.  149 

either  in  the  centre  of  the  theatre  or  at 
the  sides.  Each  fixed  heater  takes  a  cur- 
rent of  nearly  3  amperes,  at  100  volts  pres- 
sure, or  develops  an  activity  of  nearly  300 
watts,  while  the  large,  portable  heaters 
develop  1200  watts.  When  all  are  work- 
ing, the  total  activity  is  11,400  watts  or 
11.4  kilowatts.  It  is  stated,  however, 
that,  ordinarily,  only  two  of  the  large 
portable  heaters  require  to  be  used,  so 
that  the  actual  activity  employed  is  9 
KW.  The  temperature  of  the  auditorium 
is  stated  to  be  raised  20°  F.  by  these  heat- 
ers after  they  have  been  working  for  a 
reasonable  length  of  time.  The  price 
charged  being  8  cents  per  kilowatt-hour 
the  cost  of  heating  is  72  cents  per  hour, 
and  to  warm  the  theatre  for  four  hours, 
$2.88. 

It  is   similarly  proposed  to  warm  the 
stage  by  electric  heaters  to  prevent  the 


150  ELECTKIC   HEATING. 

inrush   of   cool   air  into  the  auditorium 
when  the  curtain  is  raised. 

To  secure  these  results,  it  is  only  nec- 
essary to  heat  the  air  of  the  stage  to  prac- 
tically the  same  temperature  as  that  of 
the  auditorium. 

The  advantages  possessed  by  electric 
heating,  already  pointed  out,  are  so 
marked  in  the  case  of  the  theatre,  that 
with  the  general  introduction  of  electric 
lighting  into  such  buildings,  their  electric 
heating,  either  independently  of  or  in  con 
junction  with  other  methods  of  heating, 
is  a  possibility  of  .the  near  future. 


CHAPTER  VII. 

ELECTRIC  COOKING. 

ALTHOUGH,  so  far  as  its  general  electrical 
construction  is  concerned,  an  electric 
stove  differs  in  no  respect  from  an  electric 
air  heater,  yet,  there  is  this  essential  dif- 
ference in  the  operation  of  these  two 
pieces  of  apparatus;  namely,  that  while 
the  electric  heater  is  so  arranged  as  read- 
ily to  impart  its  heat  to  a  Lirge  volume  of 
air  in  its  neighborhood,  the  electric  stove 
is  so  arranged  that  it  can  only  impart  its 
heat  to  a  small  volume  of  air  confined  in 
its  interior.  Consequently,  for  a  given 
amount  of  heat  produced,  the  air  sur- 
rounding an  electric  heater  acquires  a  tem- 
perature much  lower  than  that  within  the 
stove. 


152  ELECTRIC   HEATING. 

Suppose  any  heating  coil  be  taken,  as, 
for  example,  the  coil  shown  in  Fig.  40, 
already  described  in  connection  with  a 
car-heater  in  Fig.  24.  Let  us  suppose 
that  this  coil  has  a  resistance  of  40  ohms 
(hot).  If  a  current  of  three  amperes  be 
sent  through  it,  the  drop  in  the  coil  will 
be  3  x  40  =  120  volts,  and  the  electric  ac- 


siji 


FIG.  40.— HEATING  COIL. 

tivity  in  the  coil  3  x  120  =  360  watts,  or 
nearly  half  a  horse-power.  This  amount 
of  heat  is  capable  of  raising  the  temper- 
ature of  20  cubic  feet  of  air  1°F.  per 
second.  If  this  heater  were  placed  at 
work  in  a  closed  chamber,  the  temperature 
acquired  by  the  contained  air  would  de- 
pend upon  the  volume  of  air,  A  large 


ELECTRIC   COOKING.  153 

volume  of  air  would  acquire  a  lower  tem- 
perature than  a  small  volume  of  air.     But 
the  temperature  attained  would  not  de- 
pend only  upon  the  volume  of  air  in  the 
chamber,  but  also  upon  the  ability  of  the 
chamber  to  retain  its  heat,  that  is,  to  al- 
low no  heat  to  escape  by   conduction, 
radiation,  or  by  convection,  or  open  pas- 
sages such  as  doors,  windows,  etc.     For 
example,  'if  the  walls  of  the  chamber  were 
of  cast  iron,  the  temperature  attained  by 
the  air   within    the  chamber  would   be 
much  lower  than  if  the  walls  were  thickly 
lined  with  some  non-conductor,  such  as 
asbestos  or  felt.     If,  therefore,  wre  know 
the  volume  of  air  in  a  chamber  and  also 
the  rate  at  which  heat  escapes  from  it 
through  walls  or  apertures,  we  have  all 
the  data  necessary  for  the  determination 
of  the  resulting  temperature  of  the  con- 
tained air. 


154  ELECTRIC   HEATING. 

An  electric  oven  consists  essentially  of 
a  small  chamber,  the  air  in  which  is  prac- 
tically isolated,  the  walls  being  nearly 
air-tight  and  lined  with  some  non-con- 
ducting material,  so  as  to  retain  the  heat. 

Fig.  41  shows  a  form  of  electric  oven 
provided  with  a  wooden  external  case, 
lined  on  the  inside  with  asbestos  or  felt, 
and  covered  on  the  inside  with  bright,  tin 
plate,  which  being  a  good  reflector,  tends 
to  prevent  heat  from  being  conducted 
through  the  walls.  Two  electric  heating 
coils  are  shown  within  at  A  and  B,  respect- 
ively, one  at  the  top  and  the  other  at  the 
bottom  of  the  oven.  By  means  of  the 
switch,  shown  at  the  right  hand  of  the 
drawing,  either  or  both  can  be  operated. 
A  thermometer  is  inserted  through  a  small 
hole  in  the  top  of  the  oven,  to  show  the 
temperature  of  the  contained  air. 

Fig.  42  shows  another  form  of  electric 


ELECTRIC  COOKING.  155 

oven  with  three  separate  compartments 
and  provided  with  a  switch  for  operating 


FIG.  41.— ELECTRIC  OVEN. 

the    same.      The    large  compartment  is 
about  13  inches  wide. 


156 


ELECTRIC   HEATING. 


FIG.  42.— ELECTBIC  OVEN. 


ELECTRIC   COOKING.  157 


FIG.  43.    ELECTRIC  COFFEE  HEATER. 


158  ELECTRIC    HEATING. 

....  Fig.  43  represents  a  form  of  electric 
heater,  suitable  for  heating  a  large  quan- 
tity of  coffee  such  as  might  be  required 


FIG.  44.  -  ELECTRIC  COFFEE-POT. 

for  use  in  a  restaurant.     Here  the  heater 
coil  is  situated  in  the  base  of  the  appa- 


ratus,  out  of  contact 

ing  separated  from  the  same 

water-tight  jacket. 


FIG.  45.-  ELECTRIC  KETTLE. 

Fig.  44  represents  a  form  of  coffee-pot 
intended  to  be  heated  electrically  from  a 
pressure  of  50  or  100  volts,  absorbing,  ap- 


160  ELECTEIC    HEATING. 

proximately,  an  activity  of  500  watts. 
The  electric  heater  coil  is  contained  in  the 
base  of  the  pot.  A  flexible  cord  connects 
it  with  the  nearest  lamp  socket. 

Fig»  45  represents  a  form  of  electrically 
heated,  four -quart  tea-kettle.  This  ket- 
tle requires  an  activity  or  about  700  watts 
or  nearly  one  horse-power,  in  order  to 
boil  one  quart  of  water  in  ten  minutes. 

If  one  gallon  of  water  be  put  into  an 
electric  tea-kettle,  at  say*  a  tempera- 
ture of  41°  F.  (5°C.)  and  be  raised,  with- 
out actually  boiling,  to  the  boiling  point, 
or  100°  C.,  it  would  be  elevated  95°  C.  ; 
there  would  be,  consequently,  3786  cubic 
centimetres  elevated  95°  C.  ,  (one  gallon 
containing  3786  cubic  centimetres)  or 
3786  x  95 =359, 575  water-gramme-degrees- 
centigrade  of  heat  produced.  But  one 
calorie,  or  a  water-gramme-degree-centi- 
grade, requires  an  expenditure  of  4.18 


ELECTRKT  COOKING.  161 

joules,  so  that  the  work  required  to  be 
done  in  raising  a  gallon  of  water  to  the 
temperature  of  its  boiling  point,  would  be 
359,575  x  4.18  =  1,503,000  joules.  The  cost 
of  electric  power  in  large  quantities  is 
usually  about  8  cents  per  kilowatt-hour 
(i.  e. ,  one  KW.  supplied  for  one  hour,  or 
3,  600, 000  joules),  and,  in  very  small  quan- 
tities, 15  cents  per  kilowatt-hour. 

At  8  cents  per  KW.  hour,  the  cost  of 
raising  one  gallon  of  water  to  the  boiling 
point  would  be  3J  cents.  At  15  cents 
per  KW.  hour,  the  cost  would  be  6  £  cents. 
This  assumes,  however,  that  all  the  elec- 
trically developed  heat  is  utilized  in  rais- 
ing the  temperature  of  the  water,  which 
of  course,  is  not  the  case  since  some  heat 
is  lost.  For  example,  if  we  start  with  cold 
water  in  a  cold  kettle,  the  metal  in  the 
kettle  will  have  to  be  heated  before  its 
heat  can  be  communicated  to  the  water, 


162  ELECTRIC  HEATING. 

and,  although  in  an  air  heater,  any  heat,  so 
absorbed  in  the  mass  of  metal  of  the  heat- 
er would  be  returned  to  the  air;  in  a  wa- 
ter heater,  this  would  not  necessarily  be 
returned  to  the  water  heated;  beside,  dur- 
ing the  time  required  for  the  heating  of 
the  water,  which  would  be  about  fifteen 
minutes  for  one  gallon,  the  air  outside 
the  kettle  would  be  warmed  and  would 
carry  away  some  of  the  heat.  The  pro- 
portion of  useful  heat  developed  to 
total  heat  developed;  or,  as  it  is  called, 
the  efficiency  of  the  kettle,  would  proba- 
bly be  about  70  per  cent.  Therefore,  the 
actual  cost  of  heating  a  gallon  of  water 
would  be,  approximately,  3|  x  ifg-  =  4| 
cents  at  8  cents  per  kilowatt-hour,  or  near- 
ly 9  cents  at  15  cents  per  kilo  watt- hour. 

it  is  evident,  from  the  preceding  figures, 
that  at  the  present  price  of  electric  power, 
the  electric  water  heater  could  not  be  eco- 


ELECTEIC  COOKING.  163 

nomically  employed  on  a  large  scale.  It 
is  to  be  remembered,  however,  that  these 
prices  are  for  power  obtained  from  a  cen- 
tral station  generating  electricity  from 
coal,  through  the  intervention  of  steam  en- 
gines, boilers  and  dynamos.  With  water 
power,  the  cost  would,  probably,  be  much 
less,  and  even  with  steam  power,  where  it 
is  employed  under  the  particular  condi- 
tions applying  to  street- car  driving,  on  a 
large  scale,  the  cost  to  the  central  station 
of  a  KW.  hour  is  only  about  1J  cents. 

The  cost  of  power  developed  for  street- 
car propulsion  is  less  than  that  of  power 
developed  for  electric  lighting  for  several 
reasons.  Among  others,  to  its  being  more 
continuously  used,  and  to  its  being  man- 
ufactured on  a  larger  scale  for  street 
railway  purposes  than  for  lighting 
purposes. 


164 


ELECTRIC  HEATING. 


Fig.  46  represents  a  form  of  electric 
chafing  dish  in  which  the  electric  heat  is 
generated  from  a  resistance  coil,  placed 
in  a  water-tight  compartment  at  the  base, 
where  the  wires  enter.  The  apparatus  is 
designed  to  hold  about  one  quart  of  water, 


FIG. 46. -ELECTRIC  CHAFING  DISH. 

and  requires  to  be  supplied  with  an  activ- 
ity of  about  500  watts. 

Fig.  47  represents  an  electrically  heated 
stewing-pan  for  holding  two  quarts  and 
designed  for  a  supply  of  700  watts. 


ELECTRIC  COOKING. 


165 


It  will  be  evident,  from  an  inspection  of 
the  preceding  figures,  that,  excepting  the 
electric  stove,  all  the  different  types  of 
electric  cooking  apparatus  are  practically 
of  the  same  construction.  In  each,  an 
electric  heating  coil,  embedded  in  a  water  - 


FIG.  47.  —ELECTRIC    STEW  PAN. 

tight  manner,  in  a  suitable  part  of  the  ap- 
paratus, supplies  the  heat  that  would 
otherwise  be  obtained  from  the  ordinary 
coal  stove  or  range.  For  the  sake,  how- 
ever, of  showing  the  convenience  with 
which  an  electric  heating  coil  or  coils 


166  ELECTRIC  HEATING. 

can  be  made  to  serve  the  necessities 
of  the  culinary  art,  Figs.  48,  49  and  50, 
representing  respectively  an  electric  skil- 


FIG.  48.— ELECTRIC  SKILLET. 

let,  cake  griddle  and  cooker,  are  shown. 

In  electric  cooking  apparatus  contact 
with  the  supply  mains  is  sometimes  effect- 


FIG.  49.T--PANCAKE,  GRIDDLES. 

ed  by  the  ordinary  screw  plug.  It  is  pref- 
erable, however,  when  much  work  of 
this  character  is  to  be  done,  to  employ 


ELECTRIC  COOKING. 


167 


FIG.  50.— ELECTRIC  STEAM  COOKER. 

special  connectors  for  this  purpose.  Two 
forms  of  plug-switches  for  such  purposes 
are  shown  in  Fig.  51,  One  of  these  is  for 


168  ELECTRIC  HEATING. 

attachment  to  the  wall,  and  consists  of  a 
disc  of  wood,  or  hard  rubber,  with  a  slot 
containing  a  pair  of  separate  springs  con- 
nected with  the  supply  mains.  The  in- 
sertion plug  fits  into  the  socket  and  con- 
nects two  terminals  from  the  flexible  cord 


L       •...:__ 

FIG.  51.— PLUG  SWITCHES. 

leading  to  the  heater  with  the  spring  clip, 
thereby  establishing  the  circuit. 

The  other  switch  shows  a  very  conven- 
ient method  for  connecting  together  two 
pairs  of  flexible  cords.  Each  flexible  cord 


ELECTRIC  COOKING.  169 

terminates  in  a  cylindrical  block  of  wood 
or  rubber  in  which  is  a  pin  and  hole.  The 
pin  is  connected  with  one  terminal  and 
the  spring  metal  lining  of  the  hole  with 
the  other  terminal  of  the  supply  mains. 
The  opposite  plug  is  similarly  fitted  and 
the  two  are  united  by  placing  the  pins  in- 
to the  respective  holes  and  pressing  the 
two  together. 

Although  much  remains  to  be  accom- 
plished in  the  way  of  improvements  in 
electric  cooking  apparatus,  especially  in 
the  direction  of  producing  suitable  heat- 
ing coils  that  will  last  indefinitely  with- 
out deterioration  or  short-circuiting,  yet 
it  will  be  evident  that  the  advantages 
arising  from  the  use  of  electricity  in  the 
kitchen  are  sufficiently  great  to  warrant 
the  belief  that  this  practical  use  of  elec- 
tricity will  rapidly  grow.  An  ideal  kitch- 


170 


ELECTRIC  HEATING. 


en,  such  as  is  capable  of  being  furnished 
by    apparatus    already    in    existence,  is 


FIG.  52.  —ELECTRIC  KITCHEN. 


shown  in  Fig.  52.     Here   an  electrically 
heated   oven    is    provided  with  a  hood, 


not  to  carry  off  the 
the  odors  from  the 
switchboard  enables  the  utensils  on  the 
table  to  be  connected  with  the  supply 
mains  as  desired.  B,  is  a  hot-water  boil- 
er in  which  water  can  be  readily  heated 
electrically. 

As  we  have  already  pointed  out,  the  elec- 
tric heater,  considered  as  a  device  for 
transforming  electric  energy  into  heat 
energy,  may  be  regarded  as  an  extremely 
efficient  apparatus.  This  cannot  be  as- 
serted to  the  same  degree  of  electric  cook- 
ing apparatus,  since,  in  such  apparatus, 
some  of  the  heat  is  lost;  i.  e.,  diverted 
from  the  material  to  be  cooked,  and  sup- 
plied to  the  surrounding  metal,  air 
or  water.  Since,  however,  all  electric 
heat  is  usually  obtained  by  burning 
coal  in  a  central  station,  the  cost  of  the 


172  ELECTEIC  HEATING. 

electric  heat  on  a  large  scale  is  consider- 
ably greater  than  the  cost  of  the  heat 
necessary  for  the  same  amount  of  cook- 
ing by  the  direct  use  of  fuel  in  an  ordinary 
range. 

The  larger  the  scale  on  which  cook- 
ing is  carried  out,  the  greater  the  eco- 
nomical advantage  of  an  ordinary  fuel 
range  over  an  electric  range. 

Under  all  circumstances,  however,  the 
electric  heater  is  the  more  convenient 
and  the  more  cleanly  apparatus,  and, 
when  employed  on  a  small  scale  for  cook- 
ing, is  often  more  economical  than  a  coal 
range.  Consider,  for  example,  the  ease 
of  preparing  a  cup  of  coffee  by  electric 
heating.  Here,  there  is  only  required  the 
generation  of  an  amount  of  heat  slightly 
in  excess  of  that  required  to  bring  the 


ELECTRIC  COOKING. 


173 


water  to  the  boiling  point.  Contrast  this 
with  the  amount  of  fuel  required  to  bring 
a  cooking  range  to  the  temperature  at 
which  it  can  boil  water.  As  regards  con- 
venience everything  is  in  favor  of  the 


FIG.  53.  —SIMPLE  ELECTRIC  HEATER. 

electric  heater,  since  it  requires  only  the 
closing  of  an  electric  circuit,  which  may 
be  even  done  from  another  room,  while 
bringing  the  range  into  use,  requires  the 
lighting  of  a  fire. 


174  ELECTRIC  HEATING. 

A  simple  form  of  electric  heater  is  rep- 
resented in  Fig.  53.  Here  the  heat  is 
obtained  from  an  incandescent  lamp,  of 
size  proportionate  to  the  requirements  of 
each  case.  As  will  be  seen,  the  lamp  is 
placed  inside  the  hollow  bottom  of  a  cof- 
fee pot  or  kettle,  which  is  blackened  so 
as  to  absorb  the  heat.  In  this  way  75 
per  cent,  of  the  heat  liberated  by  the  lamp 
is  utilized  in  the  heating  of  the  water. 
It  is  claimed  that  in  the  form  shown,  a 
50 -candle-power  lamp,  of  say  200  watts 
activity,  will  heat  2  5  pounds  of  water 
to  the  temperature  of  boiling  point  in  25 
minutes,  and  that  when  the  water  is  at 
its  boiling  point  it  can  be  maintained  at 
this  temperature  by  the  activity  of  a  16- 
candle -power  lamp  (about  50  watts),  and 
in  some  cases  even  less. 

Beside    the    uses    we    have    already 


ELECTRIC  COOKING.  175 

pointed  out,  of  comparatively  small  elec- 
tric   currents   for  heating  in  connection 


PIG.  54.— ELECTRICALLY  HEATED  GLUE-POT. 

with  heaters  in  cooking  apparatus,  a  num- 
ber of  others  might  be  mentioned.  For 
example,  Fig.  54  represents  an  electric- 


176  ELECTRIC  HEATING. 

ally  heated  glue-pot,  with  a  switch  at 
the  base,  whereby  the  strength  of  current 
may  be  regulated  within  certain  limits. 
This  apparatus  requires  700  watts  for  a 
one  quart  size,  and  500  watts  for  pint 


FIG.  55.  — ELECTRIC  SAD  IRON. 

size,  when  heated  at  the  maximum  rate. 
A  much  smaller  activity  is  necessary  to 
keep  the  glue  hot  when  once  melted. 

Fig.  55  represents  a  sad  iron,  requiring 
about  250  watts  for  its  operation,  Fig.  56, 


ELECTKIC  COOKING.  177 

a  sealing-wax  heater,  and  Fig.  57,  a  curl- 
ing-long heater.  The  sad  iron  is  operated 
by  a  flexible  cord  attachment,  but  some 


FIG.  56.— SEALING  WAX  HEATER. 

forms  are  made  in  which  the  sad  iron  is 
free  from  electric  connections  and  is 
merely  laid  upon  an  electrically  heated 


FIG.  57.  —ELECTRIC  CURLING-TONGS  HEATER. 

plate  in  order  to  acquire  its  heat  by  con- 
duction. 

As  an  illustration  of  what  can  be  ef- 


178  ELECTRIC  HEATING. 

fected  in  the  direction  of  electric  cooking 
we  may  mention  a  banquet  recently 
given  in  London,  England,  by  the  direct- 
ors of  an  electric  lighting  company,  to 
120  guests,  in  which  all  the  cooking  was 
performed  electrically.  They  were  ten 
courses,  which  required  for  their  prepar- 
ation a  total  expenditure  of  energy  of  60 
kilo  watt -hours,  or  on  an  average  of  one 
half  a  kilowatt-hour  per  guest. 

The  above  company  has  notified  the 
public  that  they  w^ill  charge  8  cents  per 
kilowatt-hour  for  cooking.  Consequently, 
this  would  place  the  expense  of  such  a 
banquet  at  4  cents  per  guest  for  the  ten 
courses.  Considering  the  convenience  of 
the  process  this  charge  cannot  be  re- 
garded as  exorbitant. 

An  electrically  cooked  banquet  was  not 
a  possibility  in  the  time  of  Franklin,  yet 


ELECTKIC 

a  banquet  at  which 

insignificant  part  is  thus  humorously  de- 
scribedby  him  in  a  letter  written  in  1769: 
"Chagrined  a  little  that  we  have  been 
hitherto  able  to  produce  nothing  in  the 
way  of  use  to  mankind;  and  the  hot 
weather  coming  on,  when  electrical  experi- 
ments are  not  so  agreeable,  it  is  proposed 
to  put  an  end  to  them  for  this  season, 
somewhat  humorously,  in  a  party  of  pleas- 
ure on  the  banks  of  the  Schuylkill. 
Spirits,  at  the  same  time,  are  to  be  fired 
by  a  spark  sent  from  side  to  side  through 
the  river,  without  any  other  conductor 
than  the  water;  an  experiment  which  we 
some  time  since  performed,  to  the  amaze- 
ment of  many.  A  turkey  is  to  be  killed 
for  our  dinner  by  the  electrical  shock,  and 
roasted  by  the  electrical  jack,  before  a  fire 
kindled  by  the  electrical  bottle ;  when  the 
healths  of  all  famous  electricians,  in  En- 


180  ELECTRIC  HEATING. 

gland,  Holland,  France,  and  Germany,  are 
to  be  drank  in  electrified  bumpers,  under 
the  discharge  of  guns  from  the  electrical 
battery." 

It  may  be  of  interest  to  our  readers  to 
note  in  this  connection,  that  Dr.  Frank- 
lin was  not  devoid  of  imagination,  as  may 
be  gathered  from  a  remark  he  makes  con- 
cerning the  turkey  and  other  birds  so 
killed: 

11  He  conceited  himself  that  the  birds 
killed  in  this  manner  ate  uncommonly 
tender." 


CHAPTER  VTIL 

ELECTRIC  WELDING. 

IN  the  proportioning  of  electric  coils 
designed  for  heaters  and  cooking  appara- 
tus, care  is  taken  that  the  electric  resist- 
ance is  such  that,  with  the  electromotive 
force  employed,  the  resulting  current 
strength  should  not  be  such  that  the  coils 
shall  reach  an  unduly  high  temperature. 
In  no  form  of  such  apparatus  are  the  coils 
allowed  to  reach  an  incandescent  temper- 
ature; i.  e.,  a  temperature  at  which  they 
glow,  or  begin  to  emit  light.  There  are, 
however,  some  very  notable  applications 
of  the  heating  power  of  an  electric  cur- 
rent in  which  very  high  temperatures  are 
employed,  which  we  will  now  discuss. 


182  ELECTKIC  HEATING. 

These  are  capable  of  being  divided  into 
two  sharply  marked  classes;  namely, 

(1)  Those  in  which  a  metal    forming 
part  of  an  electric  circuit  is  raised  to  its 
welding    temperature;    that   is,    a    tem- 
perature considerably  below  the  melting 
point  of  the  metal. 

(2)  Those  in  which  metals,  or  refractory 
substances,  form  portions  of  an  electric 
circuit,  and  a  temperature  is  obtained  as 
high  as  is  possible  to  produce  under  the 
circumstances,  this  temperature  at  times 
being  the  high  temperature   of  the  vol- 
taic arc. 

Apparatus  of  the  first  type  find  their 
examples  in  various  forms  of  welding  ap- 
paratus; those  of  the  second  type,  in  elec- 
tric furnaces. 

By  the  welding  of  two  pieces  of  metal  is 
meant  causing  them  to  strongly  cohere,  or 


ELECTRIC  WELDING.  183 

hold  together  as  a  single  piece,  when  pow- 
erfully pressed  together.  Some  few  met- 
als, like  lead,  for  example,  possess  the 
power  of  welding  when  cold.  Thus,  if  two 
freshly-cut  surfaces  of  lead,  free  from 
grease  or  oxide,  are  firmly  pressed  to- 
gether, they  will  cohere  so  strongly  that 
the  welded  joint  may  be  as  strong  as  other 
portions  of  the  metal.  Other  metals,  such, 
for  example,  as  iron,  copper,  gold  and  steel, 
cannot  be  caused  to  cohere  or  weld  in 
the  cold  by  any  pressure  that  can  readily 
be  brought  to  bear  on  them.  If,  how- 
ever, these  metals  be  heated  to  their  weld- 
ing temperature,  generally  a  tempera- 
ture at  which  they  become  incandescent, 
and  then  pressed  together,  either  by  quiet 
pressure,  or  by  the  blow  of  a  hammer, 
they  readily  weld  and  cohere. 

In  order  that  welding  may  take  place  it 


184  ELECTEIC  HEATING. 

is  necessary  that  the  surfaces  of  the  metal- 
lic weld  be  clean  and  free  from  oxides  or 
other  impurities.  Such  clean  surfaces  are 
insured  by  the  use  of  a  suitable  flux,  as,  for 
example,  borax,  which  removes  the  film  of 
oxide  that  so  readily  forms  on  the  sur- 
faces of  glowing  metal. 

In  the  practical  welding  of  one  metal  to 
another,  it  has  been  found  that  the  most 
efficient  welding  is  obtained  when  a  cer- 
tain temperature  is  reached  but  not 
exceeded.  In  welding,  carried  on  by 
means  of  the  heat  of  an  ordinary  fire, 
the  operator  generally  judges  as  to 
when  this  temperature  is  reached,  by 
the  color  or  appearance  the  metal  ac- 
quires, and  much  of  the  welder's  art  con- 
sists in  his  ability  to  recognize  precisely 
when  the  proper  temperature  has  been 
reached  in  order  to  ensure  the  most 
effective  joint. 


ELECTRIC  WELDING.  185 

The  process  of  electric  welding  does  not 
differ  in  any  mechanical  point  from  the 
welding  of  metals  by  the  ordinary 
heating  process,  save,  only,  that  the  heat 
applied  to  the  welding  joint  is  of  electri- 
cal origin,  and,  instead  of  the  welding 
surfaces  being  separately  heated  in  a  fur- 
nace, and  subsequently  brought  together, 
with  the  opportunity  that  their  exposure 
to  the  air  affords  for  the  formation  of  a 
film  of  oxide  over  the  surfaces  to  be  united, 
in  the  electric  process  the  surfaces  are 
lirst  heated  by  the  passage  of  an  electric 
current  through  them  while  placed  in 
contact;  and,  when  the  welding  tempera- 
ture has  been  acquired,  which  even  for 
large  masses  of  metals  requires  only  a  few 
moments,  are  then  suitably  pressed  to- 
gether and  the  weld  is  affected. 

The  electric  process  of  welding  is  not 


186  ELECTRIC  HEATING. 

only  more  convenient  and  rapid  than  the 
ordinary  process,  but  by  its  means,  metals 
have  been  effectively  welded,  which  it  is 
impossible  to  weld  by  the  old  process. 
By  the  application  of  the  electric  welding 
process  not  only  can  the  ordinary  metals, 
such  as  iron,  steel  and  copper,  be  readily 
welded,  but  many  metals  which  required 
under  the  old  process  to  be  previously 
bronzed,  or  covered  by  a  layer  of  brass  or 
solder,  can  now  be  directly  welded.  The 
following  metals,  for  example,  have  been 
successfully  welded  electrically;  viz., 
wrought  iron,  copper,  gold,  lead,  zinc,  tin, 
silver,  aluminum  and  cast  iron,  and  some 
of  these  metals  have  even  been  welded  one 
to  another. 

The  practical  efficiency  of  any  welded 
joint,  of  course,  lies  in  the  extent  to  which 
the  tensile  strength  of  the  welded  cross- 


L 


V 


ELECTRIC 


section  equals  that  of  tHiiwelded  por- 
tions of  the  bar.  Judged 
electrically  welded  joint  possesses  a 
marked  advantage  over  an  ordinary  welded 
joint.  Tests  on  the  tensile  strength  of 
welded  bars  have  shown  generally  that 
the  bar  is  as  strong  at  the  welded  joint 
as  at  other  cross- sections,  which  is  far 
from  being  the  case  in  bars  welded  by  the 
ordinary  process,  since  the  difficulty  in  ap- 
plying the  heat  uniformly,  and  welding 
the  bar  promptly,  without  the  formation 
of  a  deleterious  scale,  is  greater  in  the 
case  of  an  ordinary  weld. 

The  current  employed  in  electric  weld- 
ing may  be  either  continuous  or  alternat- 
ing. The  amount  of  heat  liberated  in  a 
given  resistance,  by  a  given  current 
strength,  is  the  same  whether  the  current 
be  continuous  or  alternating,  although 


188  ELECTRIC  HEATING. 

large  bars,  especially  of  iron,  offer  a  great- 
er resistance  to  the  alternating  than  to 
the  continuous  current. 

It  is  possible,  therefore,  to  employ  al- 
ternating currents  for  electric  heating  and 
this  is,  indeed,  a  very  fortunate  circum- 
stance, since,  when  dynamo -electric  ma- 
chines are  employed  as  the  electric  source, 
the  use  of  the  commutator  is  thereby 
obviated;  for  alternating -current  gener- 
ators employ  no  commutator,  while 
continuous -current  machines  necessarily 
employ  one.  The  enormous  current 
strength  employed  in  welding  large  bars, 
sometimes  as  high  as  50,000  amperes, 
would  necessitate  the  use  of  massive  and 
expensive  commutators,  while  with  the 
use  of  alternating  currents  these  are 
dispensed  with. 

Extended   practical   experience  in  the 


ELECTRIC  WELDING.  189 

welding  of  metals,  especially  in  large 
masses,  has  demonstrated  the  fact  that 
not  only  does  no  inconvenience  attend  the 
use  of  alternating  currents  in  welding, 
but  that,  on  the  contrary,  such  currents 
actually  possess  advantages  over  contin- 
uous currents.  In  order  to  obtain  a  good 
joint,  a  certain  temperature  must  be  at- 
tained by  the  welding  surfaces  and  this 
temperature  should  be  as  nearly  uniform 
as  possible.  With  the  use  of  the  contin- 
uous currents  employed  in  such  cases,  the 
loss  of  heat  at  the  surfaces  of  the  metal 
causes  the  central  portions  of  the  mass  to 
attain  a  higher  temperature,  thus  render- 
ing it  more  difficult  to  obtain  a  good  weld- 
ing joint,  over  a  large  cross -section.  By 
the  use  of  alternating  currents,  however, 
a  more  uniform  distribution  of  tempera- 
ture over  the  cross -section  of  the  welded 
surfaces  is  obtained;  for,  although  as  be- 


190  ELECTBIC  HEATING. 

fore,  the  bar  necessarily  loses  its  heat 
from  the  surface,  yet,  as  is  well  known, 
alternating  currents  tend  to  develop  a 
greater  heat  at  the  surface  of  a  large  mass 
than  at  the  central  portions,  and  there  is 
thus  ensured  a  more  uniform  heating  of 
the  contact  surfaces.  Consequently,  most 
welding  processes  are  now  carried  out  by 
the  use  of  alternating  currents. 

The  apparatus  employed  in  electric 
welding  may  be  divided  into  two  classes; 
namely,  those  in  which  the  alternating 
currents  employed  are  generated  directly 
from  a  specially  designed  alternating- cur- 
rent dynamo,  and  second,  those  in  which 
the  currents  employed  are  taken  from  the 
secondary  coil  of  a  step- down  transformer, 
that  is,  a  transformer  in  which  the  sec- 
ondary terminals  supply  a  large  current 
at  a  lower  pressure,  or  a  transformer  in 


ELECTEIC  WELDING.  191 

which  the  primary  consists  of  a  long,  thin 


FIG.  58    —DIRECT  WELDER  FOR  WELDING  BABY  CARRIAGE 
TIRES  AT  THE  RATE  OF  1500  TO  3000  IN  TEN  HOURS. 

wire,  and  the  secondary  of  a  short,  stout 
wire.     The  first  method  is  called  the  proc- 


192  ELECTRIC  HEATING, 

ess  of  direct  welding,  and  the  second,  that 
of  indirect  welding. 

Fig.  58  shows  a  direct  welder  employed 
for  welding  the  iron  tires  of  baby  car- 
riages. Such  a  machine  can  make  1500  to 
2000  welds  in  ten  hours.  It  consists  of  an 
alternating- current  dynamo,  or  alterna- 
tor, with  two  field  magnets  M,  M,  and  the 
armature  A,  revolving  between  the  two 
pole-pieces,  one  on  each  side  as  shown  at 
P1.  The  armature  is  driven  by  a  belt  and 
pulley  Y.  The  armature  has  two  windings. 
One  is  connected  with  the  commutator  (7, 
at  the  end  of  the  shaft,  and  the  brushes 
B,  B,  carry  off  a  continuous,  or  commuted 
current,  to  the  field  magnet  coils  M,  M,  for 
their  excitation.  The  other  winding  on  the 
armature  consists  of  a  single  massive 
turn  of  copper  cable.  Its  extremities  are 
brought  to  the  collecting  rings  R,  R,  upon 


ELECTRIC  WELDING.  193 

which  rest  heavy  brushes  to  carry  the  pow- 
erful welding  current  to  the  two  clamps 
P,  P,  mounted  above  the  platform  F  F  F. 
These  clamps  can  be  caused  to  approach 
or  recede  by  the  turning  of  the  handle  h. 
The  clamps  P,  P,  hold  the  two  rods  d,  d 
which  are  to  be  welded  together.  The 
alternating  currents,  generated  in  the 
single  turn  of  cable  on  the  armature,  are 
carried  directly  to  the  rods  which  are 
brought  into  end -to -end  contact  by  the 
movement  of  the  clamps.  Since  the 
clamps  are  attached  to  the  rods  to  be 
welded  close  to  the  welded  ends,  it  is  evi- 
dent that  only  the  portions  between  these 
clamps  and  the  welded  surfaces,  receive 
the  welding  current  and  attain  the  welding 
temperature.  Moreover,  in  the  immediate 
neighborhood  of  the  clamps  the  heat  is 
conducted  away  into  the  large  metallic 
masses  around  the  clamps.  On  the  ap- 


194  ELECTEIC  HEATING. 

plication  of  the  current,  the  ends  of  the 
bars  to  be  welded  are  pressed  steadily  to- 
gether and  the  pressure  is  increased  as  the 
temperature  rises.  The  current  strength 
employed  in  the  welding  circuit  seldom 
exceeds  4000  amperes,  and  the  E.  M.  F.  in 
the  circuit  is  only  two  or  three  volts. 

In  order  to  avoid  the  use  of  collector 
rings  for  carrying  off  the  heavy  welding 
currents,  forms  of  direct  welders  have 
been  devised  in  which  the  armature  is  sta- 
tionary, and  the  field  is  movable.  In  this 
case,  the  ends  of  the  heavy  cable,  wound 
over  the  armature,  are  carried  directly  to 
the  welding  clamps. 

Another  form  of  direct  welder  is  illus- 
trated in  Fig.  59.  This  welder  is  spe- 
cially adapted  to  the  purpose  of  welding 
strip -iron  into  hoops.  Some  of  these  hoops 
are  represented  at  the  bottom  of  the  figure 


ELECTRIC  WELDING. 


195 


FIG.  59.— DIRECT-WELDING  APPARATUS. 


196  ELECTKIC  HEATING. 

with  their  welds  at  W.  One  of  the  mag- 
nets of  the  alternator  is  shown  at 
M.  The  pole-piece  P,  embraces  the 
armature,  which  is  driven  by  a  belt  on  the 
pulley  Y.  The  whole  machine  can  be 
moved  forward  with  the  aid  of  the  rachet 
handle  H,  so  as  to  tighten  the  belt,  when 
necessary.  The  rheostat  R,  enables  the 
strength  of  the  current  from  the  com- 
mutator C,  to  the  magnet  coils  M,  to  be 
readily  controlled.  On  the  platform  F  F, 
are  mounted  the  clamps  p  p,  connected 
with  the  ends  of  the  turn  of  cable  on  the 
armature,  through  the  collector  rings  r,  r, 
and  brushes  resting  on  the  same.  The 
strip  S,  to  be  welded,  rests  on  the  supports 
T,  is  then  cut  off  at  the  right  length  and 
thfc  two  ends  forced  under  the  clamps  p,p. 

Whenever  large  bars  or  rods  are  to  be 
welded,  indirect  welders  are  used.     Any 


ELECTRIC  WELDING.  197 

alternating- current  machine  can  be  em- 
ployed for  this  purpose.  The  machines 
usually  employed  give  an  E.  M.  F.  of  300 
volts,  with  a  frequency  of  50  cycles,  or  100 
alternations;  i.  e.,  100  reversals  of  current 
per  second.  This  alternating  E.  M.  F.  is 
led  to  the  primary  coil  of  a  step -down  al- 
ternating-current transformer,  and  the 
secondary  coil  of  this  transformer  is 
brought  directly  to  the  bars  to  be  welded. 
The  E.  M.  F.  in  the  secondary  circuit 
varies  from  1  to  4  volts,  according  to  the 
character  of  the  work  to  be  performed, 
the  strength  of  current  required,  the  melt- 
ing point  of  the  metal  to  be  welded,  the 
size  of  the  clamps,  etc. 

The  connections  of  such  an  indirect 
welder  are  represented  in  Fig.  60.  The 
alternator  A,  is  driven  by  a  belt  B.  A 
small  belt  b,  from  the  same  shaft  drives 


198 


ELECTRIC  HEATING. 


the  exciter  E,  which  supplies  the  current 
for  the  field  magnets  of  the  alternator  A, 
through  the  controlling  rheostat  R.  The 
current  from  the  collecting  rings  of  the 
alternator  armature,  is  carried  through  the 


FlG.  60,  —CONNECTIONS  OF  INDIRECT  WELDING. 

switches  S,  S,  and  the  register  g,  to  the 
primary  coil  of  the  welding  transformer  T. 
A  register  is  employed  to  count  the 
number  of  welds  that  the  machine  makes. 
The  metallic  mass  or  shell  of  the  trans- 


ELECTRIC  WELDING. 


199 


former  T,  is  grounded  by  the  ground  con- 
nection G,  in  order  to  prevent  any  shock 


FIG.  61.— CONSTANT  POTENTIAL  DYNAMO. 

from  being  accidentally  obtained  from  the 
apparatus,  by  the  operator. 

Fig.  61  represents  an  alternator,  with 
six  poles,  intended  for  indirect  welding. 
Here  a  separate  continuous  current  genera- 


200  ELECTRIC  HEATING. 

tor  6r,  supplies  current  to  the  magnets  M, 
M,  of  the  alternator.  For  this  reason  the 
alternator  is  called  a  separately -excited  ma- 
chine. There  is,  however,  on  the  alter- 
nator shaft,  a  commutator  c,  which  serves 
to  commute  part  of  the  current  from  the 
armature  A ,  and  supplies  this  rectified  or 
commuted  current  to  the  field  magnets, 
in  order  to  compensate  for  the  drop  in  the 
pressure  at  the  terminals  of  the  armature, 
when  the  machine  is  running  at  full  load. 
The  machine  is,  therefore,  said  to  be  com- 
pound-wound; i.  e.,  contains  two  separate 
windings  in  its  field  magnets.  The  rings 
r,  r,  carry  the  current  to  the  primary  coil 
of  the  welding  transformer  at  a  pressure 
of  about  300  volts.  The  handle  H,  is  for 
tightening  the  belt  on  the  main  pulley  P, 
by  driving  the  generator  forward  on  the 
guides  g,  g.  This  machine  has  a  capacity 
of  about  60  KW.,  or,  at  300  volts  pres- 


ELECTRIC  \VELDING.  201 

sure,  will   give  a  current   of   about   200 
amperes. 

Without  entering  into  a  minute  ex- 
planation of  the  function  of  an  alternating- 
current  transformer,  it  is  sufficient  to  state 
that  it  consists  essentially  of  two  coils  of 
wire,  placed  side  by  side,  called  respect- 
ively the  primary  and  secondary  coils  sur- 
rounding a  core  of  laminated  iron.  One  of 
these  coils  consists  of  many  turns  and  the 
other  of  a  few  turns.  In  the  case  of  the 
welding  transformer,  the  secondary  coil  con- 
sists of  a  single  turn  of  very  heavy  copper. 
When  a  rapidly  alternating  current,  that 
is,  a  current  which  is  rapidly  changing  its 
direction,  is  sent  through  the  primary  coil, 
currents,  alternating  equally  rapidly,  are 
generated  by  induction  in  the  secondary 
coil.  The  relation  existing  between  the 
E.  M.  F.  that  is  caused  to  act  on  the  primary 
coil  and  the  E.  M.  F.  produced  by  indue- 


202  ELECTRIC  HEATING. 

tion  in  the  secondary  coil,  will  depend  up- 
on the  relative  number  of  turns  or  loops  of 
wire  in  each.   If,  for  example,  the  primary 
contains  100  turns  and  the  secondary  a  sin- 
gle turn,  then,  if  the  E.  M.  F.  impressed 
upon  the  primary  coil  from  the  machine 
above  described  be  300  volts,  there  will  be 
induced  in  the  secondary  coil  an  E.  M.  F. 
of  about  three  volts.    But,  since  the  resist- 
ance of   this  single  turn  of  very  heavy 
copper  is  exceedingly  low,  the  resistance 
of  the  secondary  coil  may  be,  sayyi^^th 
of  an  ohm.     The  current  strength  which 
would  flow  through  the  secondary  circuit 
might,  therefore,  be  21,000  amperes,  a  cur- 
rent that  would  necessarily  possess  large 
heating  power;  namely,  3  x  21000  =  63,000 
watts  activity. 

Fig.  62  shows  a  form  of  welding  trans- 
former.    A  core  /,  of  laminated  iron,  made 


ELECTRIC  WELDING.  203 

up  of  a  number  of  thin  sheets  piled  to- 
gether, is  looped  with  a  massive  copper 
casting  S  S  S  S,  which  serves  as  a  single 


FIG.  62.— WELDING  TRANSFORMER. 

turn  of  secondary  conductor  slit  between 
the  clamps  C,C,  as  shown.  Within  the 
groove  formed  by  this  secondary  casting 


204  ELECTBIC  HEATING. 

is  placed  an  insulated  coil  of  wire  forming 
the  primary  coil,  but  not  shown  in  the  fig- 
ure. This  transformer  is,  in  reality, 
double,  a  second  transformer  being  placed 
at  the  back,  and  only  part  of  which  is 
seen.  Its  construction,  however,  is  iden- 
tical with  that  just  described.  When 
an  alternating  electric  current  is  sent 
through  the  primary  coils,  powerful  cur- 
rents are  set  up  by  induction  in  the  heavy 
single  copper  turn  forming  the  seconda- 
ries of  these  transformers  as  soon  as  their 
circuit  is  closed  through  the  clamps  and 
bars  to  be  welded. 

For  very  large  work,  which  it  would  be 
impracticable  to  bring  to  the  transformer, 
the  transformer  is  so  designed  that  it  can 
be  readily  brought  to  the -work.  For  this 
purpose  the  form  of  transformer  shown  in 
Fig.  63  has  been  devised.  The  outer  shell 


ELECTRIC  WELDING. 


205 


S  S  S  S,  of  this  transformer,  is  a  copper 
casting  made  in  two  halves  bolted  together, 
serving  as  the  secondary  coil,  and  containing 
within  it  the  primary  coil.  By  this  means 


FIG.  63. -LARGE  WELDING  TRANSFORMER. 

the  primary  coil  is  protected  from  injury. 
Insulation  is  maintained  not  only  by  in- 
sulating the  wire  of  the  primary  coil  in 
the  usual  way,  but  also  by  filling  the  inte- 


206  ELECTKIC  HEATING. 

rior  of  the  copper  box  with  oil.  The  iron 
core,  not  shown  in  the  figure,  is  linked  both 
with  the  primary  and  secondary  coils 
through  the  opening  0. 

In  order  to  decrease  the  skill  required 
for  making  an  effective  welded  joint,  the 
automatic  welder,  Fig.  64,  has  been  devised. 
Here  the  proper  degree  of  pressure  be- 
tween the  contact  surf  aces  is  automatical- 
ly applied,  amounting  for  copper  to  600 
Ibs.  per  square  inch  of  welding  cross- sec- 
tion, 1200  Ibs.  per  square  inch  for  iron, 
and  1800  Ibs.  per  square  inch  for  steel. 
The  rods  to  be  welded  are  placed  in  the 
clamps  C\  C, ,  and  are  pressed  together  by 
the  action  of  the  weight  W.  The  trans- 
former T,  supplies  from  its  secondary 
coil  the  current  strength  required  for  ef- 
fecting the  weld.  The  movement  of  the 
clamps  C,  C19  as  the  weld  is  effected, 


ELECTKIC  WELDING. 


207 


causes  a  contact  to  be  made  under  the 
control  of  the   screw  K,   actuating  the 


FIG.  64. — AUTOMATIC  WELDER. 

magnet  M,  which    interrupts  the  main 
current. 

Indirect  welders  are  made  in  a  variety 
of   forms.     Generally,  however,  the  ap- 


208  ELECTKIC  HEATING. 

paratus  is  protected  from  dirt,  dust  and  in- 
jury by  a  suitable  casing.  A  form  of 
automatic  welder  is  shown  in  Fig.  65, 
which  is  intended  for  the  welding  of 
copper  wire. 

The  amount  of  power,  which  must  be 
expended  in  effecting  a  weld,  depends 
both  upon  the  material  and  upon  its  cross - 
sectional  area.  If  we  double  the  cross - 
sectional  area,  we  increase  the  amount  of 
work  to  be  expended  by  about  150  per 
cent,  that  is  to  say,  we  more  than  double 
the  necessary  expenditure  of  work.  In 
order  to  weld  bars  of  iron  and  steel  one 
square  inch  in  cross-section,  nearly  one 
megajoule;  i.  e.,  nearly  1,000,000  joules 
must  be  expended,  or  somewhat  more 
than  1  of  a  KW.  hour.  For  a  weld  in 
brass,  of  one  square  inch  in  cross-sec- 
tion, about  the  same  amount  of  work  is 


FIG.  65.— AUTOMATIC  WELDER. 


required;  i.  e.,  a  trifle  more  than  one  mega- 
joule,  and  for  a  weld  in  copper  one  square 


210 


ELECTKIC  HEATING, 


inch  in  cross-section,  an  expenditure  of 
nearly  one  and  one -half  megajoules  is 
required. 

Fig.  66  shows  a  form  of  welder  intended 


FlG.  66.  -WELDER  FOR  CARRIAGE  TlRES. 

for  welding  carriage  tires.  The  welding 
transformer  is  situated  in  the  interior  of 
the  box  upon  which  the  clamps  are 
mounted.  Here  the  pressure  is  applied 


ELECTRIC  WELDING. 


211 


hydraulically  from  the  cylinder  G,  under 
the  action  of  the  handle  H.  The  tire  to 
be  welded  is  gripped  in  the  clamps  C,  C. 


.J 


FIG.  67.— UNIVERSAL  WELDER. 

Fig.  67  shows  a  universal  welder  adapted 
to  a  variety  of  work,  and  of  40  kilowatts 
capacity,  so  that  at  2  volts  E.  M.  F.,  the 
full-load  current  would  be  approximately 


212 


ELECTRIC  HEATING. 


20,000  amperes,  or  20  kilo -amperes.  In 
this  apparatus,  as  in  the  preceding,  the 
pressure  is  applied  hydraulically  from  the 
piston  G,  under  the  control  of  the  handle 


r 


FIG.  68.— WELTER  rcn  CARRIAGE  AXLES. 

//.     The  handles  h,  h,  are  for  operating 
the  clamps  C,  C . 

Fig.  68  shows  a  form  of  welder  suited 
for  welding  wagon  and  carriage  axles. 

Fig.  69  shows  a  welder  for  steel  wire 
cable  or  for  bars  of  iron  or  steel. 

Fig.  70   represents   a  form   of  welder 


ELECTRIC  WELDING.  213 

for  welding  steel  spokes  to  their  hubs. 
A  circular  platform  is  mounted  above 
the  transformer,  as  shown,  and  the 
four  clutches  grip  as  many  spokes  at  a 
time.  Water  is  supplied,  through  the 


FIG.  69. — WELDER  FOR  CABLE  OR  BARS. 

flexible  pipes  shown,  to  the  upper 
clamps,  which  are  hollow,  so  as  to  keep 
their  temperature  from  becoming  ex- 
cessive under  constant  use. 

Fig.  71  shows  in  detail  some  welds  ef- 


214 


ELECTRIC  HEATING. 


FIG.  70.— WELDER  FOR  WHEEL-SPOKES. 


ELECTRIC  WELDING. 


215 


fected  by  the  preceding  apparatus.  Here 
the  advantage  possessed  by  an  electric 
weld  for  telegraphic  joints  becomes  ap- 
parent. According  to  the  old  process  as 


FIG.  71.— SPECIMENS  OF  ELECTRIC  WELDING. 

shown  on  the  left  in  the  illustration,  the 
wire  was  twisted  and  soldered  as  indi- 
cated while  according  to  the  new  method 
of  welding,  the  ends  of  the  wires  are 


216  ELECTKIC  HEATING. 

abutted  and  welded  together,  as  shown  in 
the  lower  right  hand  portion  of  the  cut. 

The  extent  of  telegraphic  welds  may  be 
inferred  by  the  fact  that  a  single  firm,  man- 
ufacturing telegraphic  wire,  makes  on  the 
average  600  welds  daily  by  this  method. 
At  B  and  C,  are  shown  thin  strips  welded 
together.  At  D,  is  shown  a  welded  pipe 
which  has  been  tested  to  the  bursting 
point  and  which  has  burst  not  at  the 
weld,  but  beyond  it.  At  E,  is  a  coil  of 
pipe  containing  welded  joints;  at  F,  a  pro- 
jectile made  in  segments  and  ready  for 
welding;  at  F\  the  same  projectile  after 
welding;  G  and  H,  wire  cables  welded;  at 
K,  an  insulated  wire  with  a  welded  joint. 
Of  course,  such  welded  joints  can  only  be 
effected  conveniently  in  the  factory,  as 
the  welding  apparatus  is  not  usually  avail- 
able in  the  field. 


ELECTKIC  WELDING. 


217 


FIG.  72.— WELDER  FOB  SHRAPNEL  SHELLS. 


218 


ELECTRIC  HEATING. 


Fig.  72  shows  a  special  form  of  weld- 
ing machine  for  welding  the  hard  steel 
points  of  shrapnel  shells  to  their  soft  steel 
bodies.  This  is  an  operation  that  would 
be  very  difficult  to  accomplish  by  any 


FIG.  73. — PIPE-BENDING  APPARATUS. 

other  method.  Fig.  73  represents  a  form 
of  welding  apparatus  designed  to  heat  a 
short  length  of  pipe  to  enable  the  same  to 
be  readily  bent.  The  pipe  is  held  in  the 
screw  clamps  C,C,  and  the  current  is 


ELECTKIC  WELDING.  219 

sent  through  the  short  length  of  pipe  be- 
tween them,  w^hich  is  thus  raised  to  the 
wielding  temperature  except  in  the  imme- 
diate neighborhood  of  the  clamps. 

In  the  system  of  street  passenger  rail- 
ways, w^here  the  cars  are  driven  by  elec- 
tric motors  w^hich  take  their  current  from 
trolley  wires  and  tracks,  a  necessity  exists 
for  ensuring  a  continuous  electric  contact 
betwreen  the  separate  rails  constituting 
the  tracks.  This  is  effected,  in  practice, 
by  connecting  the  abutting  ends  of  the 
rails  by  means  of  stout  copper  wires,  or 
bonds,  as  they  are  termed.  Xo  little  diffi- 
culty has  arisen  in  practice,  owing  to  the 
imperfect  contact  thus  ensured  betwreen 
the  surfaces  of  the  bond  wires  and  the 
rail,  a  considerable  resistance  being  intro- 
duced into  the  circuit  of  the  rails  from 
this  lack  of  good  connection,  as  well  as 


220  ELECTKIC  HEATING. 

from  the  liability  to  corrosion  through 
galvanic  action.  Not  only  is  a  contin- 
uous conductor  necessary  for  the  eco- 
nomical transmission  of  electric  current 
over  the  line,  but  also  to  reduce  to  a 
minimum  the  electric  corrosion  of  the 
gas  and  water-pipes,  or  other  masses  of 
metal  situated  along  the  line  in  the 
neighborhood  of  the  railroad  tracks. 
Again,  unless  the  contact  between  adjoin- 
ing rails  is  electrically  good,  the  advan- 
tages gained  by  buried  cables,  or  ground 
feeders,  to  constitute  a  return  circuit, 
is  materially  diminished. 

An  attempt  has  been  made  to  overcome 
these  difficulties  by  rendering  the  entire 
length  of  rail  constituting  the  track  one 
continuous  metallic  conductor.  This  is 
done  by  welding  the  abutting  ends  of 
the  rails  together,  while  in  place,  on  the 


the  electric  current  has,  of 


track. 


carried  to  the  weld.  To  this  end,  the 
necessary  welding  appliances  are  placed 
on  a  special  car  which  either  takes  its 
current  from  the  trolley  wire,  or  from  any 
alternating- current  circuit  that  may  be  in 
the  neighborhood.  When  the  continuous 
current  from  the  trolley  wire  is  employed 
for  this  purpose,  the  pressure  being  ap- 
proximately 500  volts,  this  current  drives 
a  motor -dynamo,  or  rotary  transformer, 
placed  on  the  car,  and  by  this  means  the 
continuous  current  received  from  the 
trolley  is  converted  into  an  alternating 
current  and  afterward  delivered  into  the 
primary  coil  of  the  welding  transformer. 

The  car  employed  for  this  purpose  is 
shown  in  Fig.  74.  The  welding  transform- 
er, with  its  large  clamps,  is  seen  sus- 


222 


ELECTKIC  HEATltf  £. 


pended  from  a  beam  at  the  rear  end  of  the 
car.  The  same  transformer  is  shown 
more  clearly  in  Fig.  75,  which  represents 
the  welding  transformer  in  place,  in  actual 
work  upon  a  track  weld.  By  means  of  a 


FIG.  74.— TRACK- WELDING  CAR. 

motor  in  the  car,  the  surface  of  the  rails 
is  ground  by  a  revolving  grinder  for  a  few 
inches  on  each  side  of  the  joint,  so  as  to 
prepare  a  clean  surface  of  iron  on  which 
the  weld  is  to  be  produced.  Two  iron 


ELECTRIC  WELDING. 


223 


FIG.  75.  —TRACK  WELDER  AT  WORK. 


224  ELECTEIC  HEATING. 

chucks  are  then  placed  in  position,  one  on 
each  side  of  the  joint,  and  the  electric  cur- 
rent is  forced  from  the  jaws  of  the  welder 
through  the  chucks  and  across  the  two 
ends  of  the  rails.  By  this  means  the 
chucks  and  rail  ends  are  brought  to- 
gether up  to  the  welding  temperature. 
Hydraulic  pressure  is  exerted  upon  the 
chucks  by  the  hand  pump  P,  shown  on  the 
right.  When  the  weld  is  effected,  the  two 
chucks  and  the  two  ends  of  the  rail  form 
one  solid  mass.  The  massive  secondary 
copper  casting,  or  single  turn  S  S  S  S,  is 
represented  in  the  figure  with  its  two  low- 
er extremities  S^  $2  forming  the  terminals 
which  are  brought  into  contact  with  the 
chucks.  The  primary  coil  is  contained 
within  the  secondary  shell  or  box,  and 
the  laminated  iron  core  /  /,  is  passed 
through  or  linked  with  both.  The  two 
heavy  iron  jaws  J  J,  JJ,  pivoted  at  F,  are 


ELECTRIC  WELDING.  225 

drawn  apart  by  the  spiral  springs  at  the 
top,  but  are  forced  together  by  the  hy- 
draulic pump  M,  so  as  to  bring  pressure 
transversely  upon  the  chucks  through  the 
heads  of  the  secondary  terminals  St  £a . 
It  will  be  seen,  therefore,  that  the  rails 
are  not  pushed  together,  end  to  end,  but 
are  welded  transversely. 

Fig.  76  represents  the  appearance  of  a 
welded  rail,  after  the  operation  is  com- 
pleted. The  area  of  this  weld  is  from 
12  to  16  square  inches.  The  current 
strength  required  from  the  trolley  wire 
may  reach  275  amperes,  representing  an 
activity  of  about  137.5  KW.  This  is  de- 
livered from  the  motor-dynamo,  or  rotary 
transformer,  as  an  alternating  current  at 
a  pressure  somewhat  in  excess  of  300 
volts,  and,  after  allowing  for  the 
losses  of  power  in  the  rotary  transformer, 


226  ELECTEIC  HEATING. 

as  well  as    in  the  welding  transformer, 
about  120  KW.  can  be  delivered  to  the 


FIG.  76.— WELDED  RAILS. 


track,  representing  a  current  strength  of 
very  nearly  60,000  amperes.    The  welding 


ELECTRIC  WELDING.  227 

transformer  is  oil-insulated,  so  that  the 
whole  apparatus  can  be  worked  in  the 
rain.  Water  is  circulated  through  the 
jaws,  in  order  to  cool  them  when  at  work. 
Under  favorable  circumstances,  four  joints 
can  be  made  per  hour. 

A  street  rail,  weighing  70  Ibs.  per  yard, 
when  prevented  from  expanding  and  con  - 
tracting,  owing  to  the  entire  rail  being  in  a 
single  length,  requires  about  150,000  Ibs. 
tensile  strength  to  withstand  the  stresses 
produced  in  it  by  the  expansions  and 
contractions,  following  changes  in  tem- 
perature due  to  the  seasons.  An  elec- 
tric weld  requires  more  than  250,000 
pounds  to  break  it.  Consequently,  a 
track  is  not  likely  to  break  at  a  weld 
owing  to  the  stresses  produced  by  tem- 
perature variation.  It  is  necessary,  how- 
ever, in  practice,  to  keep  the  track  firmly 


228  ELECTRIC  HEATING. 

from    bending   in    summer,    by   securely 
fastening  it  to  the  sleepers. 

In  order  to  cite  an  example  of  the 
practical  application  of  electric  track 
welding,  it  may  be  mentioned  that  in  th^ 
city  of  Boston,  four  miles  of  Providence 
girder  street  car  rails,  weighing  61  Ibs. 
per  yard,  were  electrically  welded  in  the 
summer  of  1893  in  one  continuous  length. 
It  had  been  the  general  belief,  up  to  the 
date  of  this  experiment,  that  a  track  so 
welded  could  not  resist  the  tendency  of 
its  own  expansion  and  contraction  to  pull 
it  to  pieces.  These  four  miles  remained 
in  good  condition  until  the  following 
winter,  when  they  broke  in  about  80 
places,  but,  in  nearly  all  cases,  it  is  inter- 
esting to  note  that  these  fractures  did  not 
occur  at  the  joints,  but  about  four  to  eight 
inches  from  them.  These  fractures  were 


ELECTRIC  WELDING.  229 

repaired  by  being  electrically  welded. 
The  track  lasted  intact  through  the  sum- 
mer of  1894,  but  again  broke  the  following 
winter  in  about  30  places.  It  is  a  curious 
fact  that  these  breaks  did  not  occur  at 
regular  intervals,  but  several  would  usu- 
ally appear  within  a  few  feet,  and  then 
none,  perhaps,  for  half  a  mile.  It  is 
claimed  that  the  difficulty  referred  to  in 
the  preceding  paragraph  can  now  be 
overcome. 

In  all  the  methods  of  welding  thus  far 
described,  a  single  process  is  employed; 
namely,  the  parts  to  be  welded  are 
brought  into  contact  and  a  powerful 
electric  current  is  sent  through  the  con- 
tact surfaces  until  they  are  raided  to  the 
welding  temperature.  The  temperature 
is  never  allowed  to  reach  the  fusing  point. 
Another  method  of  welding,  which  dif- 


230  ELECTRIC  HEATING. 

fers  radically  from  the  preceding,  consists, 
practically,  in  bringing  the  metals  to  be 
welded  to  the  fusing  point.  This  is  ac- 
complished by  the  use  of  the  voltaic  arc 
as  follows ;  one  terminal  of  the  source  of 
current,  preferably  a  storage  battery  of 
between  50  and  100  volts  E.  M.  F.,  is  con- 
nected to  the  metals  to  be  welded,  and 
the  other  terminal,  to  a  rod  of  hard  carbon, 
which  is  brought  into  contact  at  the  weld- 
ing surfaces  and  then  separated  a  short 
distance  fi'om  them,  so  as  to  form  an  arc 
between  the  metal  and  the  end  of  the  car- 
bon electrode.  By  this  means,  a  partial 
fusion  is  obtained,  which  results  in  an 
electric  soldering-,  or,  as  it  is  sometimes 
called,  a  welding  at  the  joint.  This  meth- 
od of  uniting  the  ends  of  metal  bars  or 
rods,  is  not  unlike  the  burning  process  as 
applied  to  lead,  in  which  two  abutting  sur- 
faces or  ends  of  lead  sheets  are  united  by 


ELECTRIC  WELDING.  231 

the  aid  of  a  blow-pipe  flame.  It  is  evi- 
dent that  this  method  is  not  capable  of  as 
many  applications  as  is  the  method  pre- 
viously described,  since  the  heat,  being 
only  superficially  applied,  is  incapable  of 
giving  to  joints  of  any  considerable  cross- 
section,  that  uniformity  of  temperature  on 
which  a  good  weld  is  dependent.  The 
process,  however,  possesses  some  advan- 
tages, and  has  been  successfully  applied 
to  the  filling  of  blow  holes  in  castings.  It 
is  evident  that  masses  of  metal  intro- 
duced at  the  fusing  temperature  into  such 
blow  holes,  under  the  action  of  the  elec- 
tric arc,  tend  to  render  the  mass  of  metal 
fairly  homogeneous,  provided  the  precau- 
tion has  been  taken  to  previously  heat 
the  casting  to  a  dull  redness. 

The  same  process  has  been  applied  to 
longitudinal  welding^  or  calking  of  plates 


232  ELECTRIC  HEATING. 

that  have  already  been  riveted,  in  order  to 
make  a  water-tight  joint  and  instead  of 
employing  a  calking  tool.  As  before, 
however,  the  process  is  limited  to  the 
case  of  comparatively  thin  plates . 

Another  method,  also  dependent  on  the 
heat  of  the  voltaic  arc,  consists  in  de- 
flecting, by  the  aid  of  an  electromagnet, 
the  arc  existing  between  two  carbon  points 
and  directing  the  flame  against  the  sur- 
faces to  be  welded.  This  apparatus  con- 
stitutes, in  fact,  an  electric  blow-pipe. 


CHAPTER  IX. 

ELECTRIC  FURNACES. 

THE  intense  heat  of  the  voltaic  arc, 
forming,  as  it  does,  the  most  powerful 
source  of  heat  known,  led  many  investi- 
gators, at  a  very  early  date,  to  apply  it 
in  various  metallurgical  processes.  These 
processes  were,  as  a  rule,  carried  out  in 
what  may  be  properly  styled  electric  fur- 
naces. That  is,  in  furnaces,  the  heat  of 
which  was  obtained  electrically,  either  by 
means  of  the  voltaic  arc,  or  by  the  heat  of 
intense  incandescence  of  such  refractory 
substances  as  graphite  or  carbon.  It  may 
be  well  to  point  out,  in  this  connection, 
that  the  electric  furnace  differs  radically 
from  any  furnace  in  which  the  heat  is  ob- 
tained by  ordinary  combustion,  in  that 


234  ELECTRIC  HEATING. 

means  must  necessarily  be  provided,  in 
the  combustion  furnaces,  for  carrying  off 
the  products  of  combustion.  This  not 
only  ensures  an  inefficient  form  of  fur- 
nace, but  also  necessitates  the  cooling 
or  chilling  of  the  furnace  by  the  loss  of 
heat,  and  by  the  ingress  of  cold  air.  In 
marked  contrast  with  this,  in  an  elec- 
tric furnace,  no  essential  gaseous  prod- 
ucts of  combustion  are  formed  in  the 
production  of  the  heat,  and,  consequent- 
ly, all  the  heat  developed  is  retained, 
with  the  exception  of  such  losses  as  occur 
through  the  walls  of  the  furnace  by  con- 
duction. Electric  furnaces  have  been 
known  in  the  art  as  early  as  1848,  and 
since  that  time  have  been  very  frequently 
employed. 

The  electric  furnace  assumes  a  variety 
of  forms,  one  of  which  is  shown  in  Fig.  77. 


ELECTRIC 

Here  a  voltaic  carbon 
the  source  of  heat,  the  arc  being 
mitted  to  play  in  the  interior  of  a  crucible 
of  refractory  material,  surrounded  by  a 
non-conducting  mass,  usually  of  fire- 


Pio. 


— ELECTRIC  FURNACE. 


brick.  Since  comparatively  little  heat 
escapes  by  conduction,  the  temperature 
which  may  be  attained  in  the  interior  is 
exceedingly  high.  This  particular  form  of 
furnace  was  employed  to  ascertain  the 
temperature  at  which  carbon  boils. 


236  ELECTBIC  HEATING. 

Although  constructed  in  a  variety  of 
forms,  all  electric  furnaces  may  be  di- 
vided into  two  classes;  namely,  lirst,  those 
in  which  the  operations  carried  on  are 
effected  by  means  of  the  intense  heat 
electrically  produced,  and,  second,  those 
in  which  the  operations  are  effected  by 
electrolysis;  i.e.,  the  power  possessed  by 
an  electric  current,  under  certain  con- 
ditions, of  effecting  chemical  decomposi- 
tions. By  far,  however,  the  greater  num- 
ber of  commercial  electric  furnaces 
belong  to  the  first  class. 

In  all  electric  furnaces  the  heat  is 
obtained  either  by  means  of  the  electric 
arc  or  by  electric  incandescence.  Since 
carbon  is  one  of  the  most  refractory  sub- 
stances known,  it  is  generally  employed 
either  as  the  material  between  which  the 
arc  is  formed,  or  as  the  substance  for 


ELECTRIC  FURNACES.  237 

leading  the  current  into  the  furnace. 
Since,  as  is  well  known,  the  carbon  arc  is 
the  most  intense  source  of  artificial  heat 
we  possess,  and  the  peculiar  construction 
of  the  electric  furnace  permits  this  heat 
to  be  readily  accumulated,  the  tempera- 
ture reached  is  the  highest  artificially 
obtainable.  Consequently,  under  these 
conditions,  chemical  processes  become 
possible  on  a  commercial  scale,  that  here- 
tofore could  only  be  conducted  on  a 
small  scale  in  laboratory  research. 

As  an  example  of  a  commercial  process 
carried  on  under  the  intense  heat  of  the 
electric  furnace,  we  may  mention  the 
manufacture  of  a  compound  of  silicon  and 
carbon,  known  in  commerce  as  carborun- 
dum. This  material  is  carbon  silicide,  a 
molecule  of  which  consists  of  an  atom  of 
silicon  united  to  an  atom  of  carbon.  This 


238  ELECTRIC  HEATING. 

product  is  of  considerable  commercial 
value  in  the  arts,  owing  to  its  great  hard- 
ness, and  is  extensively  used  as  an  abra- 
sive material,  as  a  substitute  for  emery  and 
corundum,  and  has  even  been  employed 


FIG.  78. — LONGITUDINAL  SECTION  OF  CARBORUNDUM  FUR- 
NACE. 

in  the  place  of  diamond   dust,    for  the 
polishing  of  gems. 

The  furnace  employed  for  the  produc- 
tion of  carborundum  is  shown  in  longi- 
tudinal section,  as  charged  ready  for  the 
passage  of  the  current,  in  Fig.  78.  It 


ELECTRIC  FURNACES.  239 

consists  substantially  of  a  rectangular 
chamber,  whose  walls  are  formed  of  brick 
and  fire-clay.  The  furnace  chamber  is 
charged  with  a  central  core  of  granular 
coke,  surrounded  by  a  mixture  of  carbon, 
sand,  salt  and  sawdust.  In  order  to  ef- 
fectively connect  the  electric  source  with 
the  central  carbon  core  of  the  charged 
furnace,  carbon  rods  or  terminals  are 
placed  at  each  end  of  the  furnace  and 
brought  into  good  electrical  connection 
with  the  core  by  means  of  a  filling  of  fine 
carbon  tightly  packed  around  them. 
When  a  powerful  electric  current  is  sent 
through  this  furnace,  a  chemical  action 
occurs,  under  the  influence  of  the  intense 
heat,  whereby  a  combination  is  effected 
between  the  carbon  mainly  of  the  central 
core  and  the  silicon  of  the  sand,  with  the 
formation  of  a  silicide  of  carbon  called 
carborundum. 


240 


ELECTRIC  HEATING. 


A  cross-section  of  the  furnace,  prior  to 
the  passage  of  the  current,  is  shown  in 
Fig.  79,  and  another  cross-section,  after 
the  passage  of  the  current,  in  Fig.  80. 
Eeference  to  the  latter  figure  will  show 


FIG.  79.  -SECTION  THROUGH  FURNACE  BEFORE  PASSAGE  OF 
CURRENT. 

that  a  portion  of  the  coke  core  still  re- 
mains unaltered,  while  carborundum  in 
the  crystalized  and  uncrystalized  states 
surrounds  this  unaltered  core. 


Another  commercial  application  of  the 


ELECTRIC  FURNACES. 


241 


electric  furnace  in  which  the  product  is 
obtained  by  high  temperature,  is  in  the 
process  for  the  manufacture  of  calcium 
carbide.  In  this  process  the  product  is 
obtained  by  the  prolonged  action  of  an 


CARBORUNDUM,  NOT  CRYSTALLIZED  - 

CARBORUNDUM  CRYSTALS  

COKE  CORE 


FIG.  80.— SECTION  THROUGH    FURNACE  AFTER  PASSAGE  OF 
CURRENT. 

electric  arc  on  a  mixture  of  lime  and  car- 
bon, placed  inside  a  suitably  formed 
smelting  furnace,  formed  of  refractory 
materials.  The  form  of  the  furnace  is 
shown  in  Fig.  81.  The  outer  shell  A, 


242 


ELECTRIC  HEATING. 


consists  of  a  cylindrical  fire -brick  cover  or 
bench,  inside  of  which  is  placed  a  crucible 
B,  of  carbon  or  graphite.  Both  the  cruci- 


FIG.  81.— FURNACE  FOR  PRODUCTION  OF  CALCIUM  CARBIDE. 

ble.Z?,  and  the  masonry  A,  rest  on  a  con- 
ducting plate  6,  of  metal,  to  which  one  of 
the  terminals  of  the  dynamo  is  connected, 
the  other  terminal  being  connected  to  the 


ELECTRIC  FURNACES.  243 

carbon  bar  or  pencil  C,  forming  the  mova- 
ble electrode  of  the  furnace.  The  furnace 
is  provided  with  the  cover  E,  formed  of  a 
single  or  double  carbon  plate.  This  is  in- 
sulated from  the  body  of  the  furnace  B, 
by  means  of  a  plate  of  non-conducting 
material  F.  The  material  to  be  acted  on 
is  placed  at  the  bottom  of  the  furnace, 
and  heat  applied  by  means  of  a  current 
passing  between  the  electrode  C,  and  the 
crucible  B.  A  screw-thread  shaft  G,  at- 
tached to  the  carbon,  permits  the  adjust- 
ment of  the  central  electrode  in  the  nut 
h.  A  tap  hole  is  provided  at  d,  for  dis- 
charging the  products  of  the  furnace  from 
time  to  time.  During  operation,  this  hole 
is  closed  by  a  plug  of  clay  or  other  suit- 
able material. 

An  alternating  current  of  from  4000  to 
5000  amperes  under  a  pressure  of  from  35 
to  25  volts,  representing  an  activity  of 


244  ELECTRIC  HEATING. 

about  135  KW.,  or  180  H.P.,  can,  it  is 
claimed,  produce  daily  in  such  furnaces  a 
yield  of  one  short  tori,  or  2000  pounds  of 
calcium  carbide  at  a  cost  of  about  $15. 

No  little  attention  has  recently  been  at- 
tracted to  the  preparation  of  calcium  car- 
bide, from  the  fact  that  when  thrown  into 
water,  it  is  capable  of  yielding  acetylene 
gas,  a  combination  of  hydrogen  and  carbon 
(C2H2),  which  possesses  a  high  illumi- 
nating power  when  burnt  in  air.  Either 
a  continuous  or  an  alternating  current 
may  be  employed  in  its  production.  One 
of  the  most  important  uses  to  which 
acetylene  can  be  applied  is  the  enrich- 
ment of  ordinary  illuminating  gas,  so  as 
to  increase  its  light-giving  power. 

Up  to  the  present  time,  perhaps,  the 
most  important  application  of  the  electric 


ELECTRIC  FURNACES. 


245 


furnace  is  to  the  production  of  aluminium, 
either  pure  or  alloyed  with  copper. 

Fig.  82  represents  a  section  of  an  elec- 
tric furnace  which  produces  aluminium 
bronze  alloy;  i.  e. ,  aluminium  alloyed  with 
copper.  This  furnace  consists  essential- 
ly of  a  rectangular  chamber  of  fire-brick 


FIG.  82.  —ELECTRIC   FURNACE    FOB    THE    PRODUCTION    OF 
ALUMIMUM  ALLOYS. 

provided  with  carbon  electrodes  entering 
the  charged  chamber. 

A  convenient  size  for  such  a  furnace  has 
an  interior  length  of  five  feet,  a  width  of 
one  foot,  and  a  height  of  one  foot.  The 
charge  occupies  the  centre  of  this  space  in 
a  mass  roughly  3  feet  long,  7  inches  wide 
and  3  inches  high,  the  space  between 


246  ELECTRIC   HEATING. 

the  charge  and  the  wall  being  filled  with 
limed  charcoal.  The  furnace  employs  a 
carbon  arc  as  the  source  of  heat,  the  arc 
being  formed  between  the  carbon  elec- 
trodes which  lead  the  current  through  the 
furnace.  In  the  figure  these  electrodes 
are  shown  at  A-r  A — ,  the  arc  being  formed 
between  them  at  D.  The  electrodes  pass 
through  openings  in  the  ends  through 
boxes  B,  Bl ,  filled  with  granulated  copper. 
The  charge  in  such  a  furnace  is  frequently 
a  mixture  of  50  Ibs.  granulated  copper, 
with  25  Ibs.  of  crushed  cryolite,  a  mineral 
rich  in  aluminium,  and  12  Ibs.  of  charcoal. 
The  current  strength  varies  from  1200  to 
1500  amperes,  and  is  maintained  at  a 
pressure  of  about  50  volts  for  5  hours. 
Under  these  circumstances,  the  ore  of 
aluminium  is  reduced  in  the  presence  of 
highly  heated  carbon,  and  the  reduced 
metal  enters  into  an  alloy  with  the  molt- 


ELECTRIC 


en  copper.  When  thc^fi^iace  is  cleared, 
50  Ibs.  of  alloy  are  obtam^L having. r  from 
15  to  35  per  cent,  of  aluminftrm- aad  a 
small  quantity  of  silicon. 


In  another  process,  by  means  of  which 
the  aluminium  is  obtained  in  a  pure  state, 
the  decomposition  is  effected  by  elec- 
trolysis. Here  the  current  is  led  through 
an  electrolytic  bath  of  alumina  dissolved 
in  a  double  fluoride  of  aluminium  and 
potassium,  maintained  in  a  fused  state  by 
the  heat  evolved  during  the  passage  of 
the  current.  In  one  process  in  which 
this  is  effected,  the  crucible,  which  con- 
sists of  an  iron  box  suitably  lined  with 
carbon  forming  the  cathode  or  negative 
electrode,  is  charged  with  the  ores  of 
aluminium,  and  a  carbon  rod,  standing 
vertically  in  the  centre,  forms  the  anode, 
or  positive  electrode.  The  current  enters 


248  ELECTRIC  HEATING. 

by  this  carbon  rod,  and,  after  passing 
through  the  materials  of  the  furnace, 
leaves  it  at  the  negative  or  external  sur- 
face by  means  of  the  iron  frame  suitably 
connected  to  the  other  pole  of  the  dyna- 
mo. The  current  strength  employed  is 
about  3500  amperes  at  a  pressure  of  ap- 
proximately 35  volts,  representing  an  ac- 
tivity of  122.5  KW.  The  furnace  is  so 
arranged  that  the  metal  can  be  tapped  off 
and  withdrawn  as  it  is  formed,  so  that 
the  process  is  a  continuous  one,  fresh  ore 
being  added  from  time  to  time.  The  effect 
of  the  current  is  not  only  to  keep  the 
charge  in  the  furnace  molten  by  the  heat 
produced  in  the  passage  through  the  fur- 
nace, but  also  to  reduce  the  metal  from 
the  ore  by  electrolytic  action.  By  these 
means  the  metal  obtained  is  very  nearly 
pure.  The  iron  box  is  usually  cubical  in 
shape,  and  is  two  feet  deep.  It  has  an 


ELECTRIC  FURNACES.  249 

opening  beneath,  which  is  supplied  with  a 
plug  of  carbon  or  clay  to  permit  of  the 
pouring  off  of  the  metal. 

The  electric  furnace  has  been  employed 
in  obtaining  a  number  of  rare  metallic 
substances  among  which  chromium  may 
be  mentioned. 

In  the  use  of  electric  furnaces  for  me- 
tallurgic  purposes  many  advantages  arise 
from  the  fact  that  a  vacuum  can  readily  be 
maintained  within  the  furnace  during  the 
operation.  For  this  reason  metals  ob- 
tained in  the  fused  state  from  their  ores 
by  electric  reduction,  or  metals  fused 
in  air-tight  furnaces  by  the  application 
of  heat  of  electric  origin,  produce  sharper 
and  much  more  homogeneous  castings 
than  those  melted  when  exposed  to  the 
air.  Moreover,  such  castings  are  devoid 
of  troublesome  blow  holes  and  blasts, 
and  are  denser  than  ordinary  castings. 


250  ELECTKIC    HEATING. 

In  one  form  of  electric  furnace,  the  ore 
is  not  only  reduced  to  the  metallic  state, 
by  the  action  of  the  current,  but  is  also 
cast  directly  from  the  furnace,  within 
which  a  vacuum  is  maintained.  This  fur- 
nace consists  of  an  air-tight  chamber,  pro- 
vided with  an  inclined  hearth,  arranged  so 
as  to  permit  the  reduced  and,  molten 
metal  to  flow  directly  from  the  furnace 
into  the  mould  when  so  desired.  The 
chamber  of  the  furnace  is  filled  with  a 
suitable  mixture  of  ore,  flux  and  redu- 
cing agent,  and  subjected  to  the  influence 
of  the  electric  current;  or,  the  furnace  is 
given  a  charge  of  the  metal  to  be  melted 
and  a  current  applied  sufficient  to  melt 
it,  while  in  the  presence  of  a  vacuum. 

The  practical  limit  of  size  proposed  for 
such  a  chamber  is  40  feet  in  length  and 
capable  of  holding  1 J  tons  of  metal  at  a 


ELECTKIC  FUKNACES.  251 

charge.  By  working  such  a  chamber  with 
a  current  of  about  30,000  amperes,  at 
fifty  volts  pressure ;  i.  e. ,  at  an  activity 
of  about  1500  KW.,  somewhat  less  than 
the  activity  already  employed  in  the  alu- 
minium electric  furnace  at  Xeuhausen, 
the  entire  charge  can  be  fused  and  run  off 
in  about  a  quarter  of  an  hour.  Such  a 
furnace  would,  therefore,  be  capable  of 
turning  out  a  ve?y  large  number  of  cast- 
ings in  a  single  day. 

It  might  be  supposed  that  the  electric 
melting  of  metals  would  be  more  expen- 
sive than  the  ordinary  method  employing 
the  regenerative  furnace,  but,  bearing  in 
mind  the  fact  that  all  the  heat  developed 
by  the  electric  current  can  be  liberated 
exactly  where  it  is  wanted,  and  that  the 
loss  of  heat  in  such  a  furnace  is  very  small, 
it  is  evident,  that  even  where  water-power 


252  ELECTRIC  HEATING. 

is  not  obtainable,  this  method  might  com- 
pete with  coal  on  a  commercial  basis. 
For  example,  it  has  been  estimated  that 
in  order  to  smelt  a  short  ton  of  iron  in 
the  Siemens -Martin  regenerative  furnace, 
from  1000  to  1400  pounds  of  coal  are  re- 
quired. By  the  electric  process  here  de- 
scribed, assuming  that  coal  is  burned  to 
drive  the  dynamo  and  operate  the  air 
pump  employed  in  maintaining  the  vac- 
uum, the  same  work  can,  it  is  claimed,  be 
done  by  the  consumption  of  from  720  to 
800  Ibs.  of  coal. 

In  the  use  of  a  furnace  of  the  above 
type  for  the  direct  production  of  pig  iron 
from  iron  ore,  the  resulting  iron  can  be 
made  to  contain  much  less  carbon  that  in 
that  produced  by  the  ordinary  blast  fur- 
nace, since  the  ingredients  can  be  much 
more  closely  proportioned  in  the  elec- 


ELECTRIC  FURNACES.  253 

trie  furnace  than  in  the  ordinary  blast 
furnace.  Experiments  made  have  pro- 
duced pig  iron  containing  less  than  3  per 
cent,  of  total  carbon. 

The  electric  furnace  has  been  employed 
for  the  artificial  production  of  very  small 
diamonds.  When  carbon  is  melted  and 
vaporized  in  the  electric  furnace,  it  con- 
denses in  the  form  of  graphite  with  the 
specific  gravity  of  about  2.  Indeed  this 
same  process  occurs  in  every  arc  lamp,  the 
carbon  being  volatilized  at  the  positive 
electrode,  a  portion  of  this  vapor  con- 
densing in  the  form  of  a  nipple  of  graph- 
ite on  the  cooler,  negative  or  opposite 
electrode.  In  order  to  produce  the  dia- 
mond, great  pressure  is  necessary.  This 
can  be  obtained  by  forming  a  solution  of 
carbon  in  molten  iron,  and  allowing  the 
iron  to  solidify  suddenly,  thereby  bring- 


254  ELECTBIC  HEATING. 

ing  sufficient  pressure  upon  the  contained 
carbon  to  crystalize  the  latter  into  dia- 
monds. A  molten  solution  of  carbon  and 
iron,  obtained  in  an  electric  furnace,  is 
suddenly  poured  into  lead  that  has  just 
been  separately  melted.  The  iron  and 
carbon,  being  lighter  than  molten  lead, 
float  to  its  surface  in  the  form  of  globules, 
and  solidify.  These  globules,  when  dis- 
solved in  suitable  acids,  will  leave  as  a 
residue  the  diamond  crystals  which  are 
unfortunately  very  minute,  but  have  all 
the  physical  properties  of  larger  natural 


CHAPTER  X. 

MISCELLANEOUS    APPLICATIONS    OF     ELECTRIC 
HEATING. 

BESIDE  the  different  commercial  appli- 
cations of  heat  of  electric  origin,  which  we 
have  already  described,  there  are  others  of 
great  interest  that  would  appear  to  have 
a  reasonable  probability  of  coming  into  ex- 
tensive use  in  the  near  future.  We  will, 
therefore,  devote  the  consideration  of  the 
closing  chapter  to  some  of  the  more  inter- 
esting of  these  applications. 

In  the  manufacture  of  harveyized  armor 
plates,  now  extensively  employed  on  war- 
ships, considerable  difficulty  has  arisen  in 
drilling  the  plates  so  as  to  permit  them  to 
be  riveted  together.  The  harveyized  steel 


256  ELECTBIC  HEATING. 

plate,  as  is  well  known,  is  so  extreme- 
ly hard,  that  the  ordinary  drill  has  no 
effect  whatever  on  it.  Attempts  have 
been  made  to  soften,  or  anneal,  these 
plates  at  the  points  where  the  drill  holes 
have  to  be  made,  but  although  the  intense 
heat  of  the  oxy -hydrogen  blow -pipe  has 
been  tried  for  this  purpose,  it  has  been 
found  to  be  insufficient.  For  this  reason 
a  strip  around  the  edges  of  the  plate  had 
to  be  left  unhardened,  so  as  to  permit  of 
the  drilling,  and  this  was  an  element  of 
weakness.  It  has  been  found,  however, 
that  under  the  intense  heat  of  the  voltaic 
arc,  even  the  harveyized  plate  was  an- 
nealed, or  restored  to  the  soft  condition, 
then  readily  permitting  penetration  by 
the  drill.  This  method  of  electric  anneal- 
ing is  carried  out  specifically  as  follows: 
Blocks  of  copper  are  laid  on  the  surface 
of  the  plate  and  connected  with  an  alter- 


MISCELLANEOUS  APPLIB&HQNS.  257 

"\ 


nating  current  transformer, 
welding  transformer.  By  this  meansTcftr~ 
the  passage  of  the  current,  intense  heat 
is  developed  in  the  plate  between  the  two 
electrodes  or  masses  of  copper.  The 
temperature  is  then  slowly  lowered  by  re- 
ducing the  current  strength.  This  has 
the  effect  of  withdrawing  the  temper,  or 
annealing  the  plate  between  the  two 
blocks  of  copper.  It  has  been  found  that 
alternating  currents  are  more  favorable 
for  the  concentration  of  the  heating  effect 
than  continuous  currents,  a  fact  due  to 
the  inductance  in  the  iron. 

The  heat  of  the  voltaic  arc  has  been  em- 
ployed in  a  process  of  electric  casting  al- 
ready described  and  mentioned  as  a  proc- 
ess of  electric  soldering.  This  process  is 
applicable  to  the  cases  of  repairing  fly- 
wheels, steam  cylinders,  connecting-rods, 


258  ELECTHIC  HEATING. 

etc.  It  consists  essentially  in  the  em- 
ployment of  the  voltaic  arc  taken  be- 
tween two  metal  electrodes.  One  of  the 
electrodes,  consisting  of  the  mass  of  the 
metal  to  be  repaired,  is  fixed,  and  the 
other,  the  movable  electrode,  is  made  of 
the  metal  which  is  to  be  fused  and  em- 
ployed in  the  repairing.  Under  these 
conditions,  the  arc  is  formed  between  the 
metal  to  be  repaired  and  the  metal  em- 
ployed in  the  casting  or  filling  of  the 
intervening  space,  the  latter  melting, 
and  dropping  into  the  interstices  of  the 
metal  to  be  filled  with  the  metal  and 
then  soldered  or  welded. 

This  process  requires  about  8  amperes 
per  active  square  millimetre  of  the  metal 
electrode.  The  usual  diameter  em- 
ployed for  the  electric  soldering  tool  is 
from  6  to  10  millimetres.  It  is  neces- 
sary that  the  metal  which  receives  the 


MISCELLANEOUS  APPLICATIONS.         259 

molten  application  should  itself  be  raised 
to  a  red  heat,  as,  otherwise,  the  molten 
metal  introduced  would  chill  too  rapidly, 
and  thus  prevent  an  effective  junction. 

Probably  one  of  the  most  valuable  mis- 
cellaneous applications  of  electric  heating 
is  to  be  found  in  the  various  processes 
which  have  been  designed  for  the  electric- 
al working  and  forging  of  metals.  In  these 
processes,  the  metal  is  brought  by  heat  of 
electric  origin  to  the  temperature  re- 
quired for  its  working,  shaping  or  forging. 

In  this,  as  in  other  commercial  applica- 
tions of  electric  heating,  one  of  the  most 
marked  advantages  obtained  is  found  in 
the  fact  that  the  heat  is  developed  in  the 
exact  locality  where  it  is  needed,  and  not 
elsewhere;  is  developed  only  to  the  ex- 
tent it  is  needed,  and  not  to  an  unneces- 
sary extent;  and,  moreover,  only  at  the 


260  ELECTRIC  HEATING. 

time  when  it  is  needed.  Instead  of  re- 
quiring a  long  previous  heating  in  the 
forge  or  furnace  with  a  waste  of  fuel,  the 
metal  is  quickly  heated  by  the  electric 
current.  Moreover,  heat  of  electric  ori- 
gin is  capable  of  much  finer  and  closer 
regulation  than  is  heat  of  the  ordinary 
forge  or  furnace.  Then  again,  automatic 
devices  may  be  readily  introduced  where- 
by the  current  can  not  only  be  controlled 
as  to  amount,  but  also  can  be  cut  off  as 
soon  as  a  certain  temperature  is  reached. 
This  will  be  found  a  matter  of  consider- 
able advantage  in  cases  where  the  metals 
to  be  worked  require  tempering,  since 
the  heat  to  which  they  are  subjected 
can  be  made  absolutely  uniform,  irre- 
spective of  the  size  of  the  piece  to  be 
heated.  Moreover,  the  bar  can  be  heated 
uniformly  throughout  all  portions  of  its 
area  of  cross-section, 


MISCELLANEOUS  APPLICATIONS.          261 

A  decided  advantage  in  electric  forging 
lies  in  the  rapidity  with  which  the  heating 
can  be  obtained;  for,  if  the  power  applied 
be  ample,  the  bar  to  be  forged  can  be 
brought  up  to  the  forging  temperature  in 
less  than  a  minute.  At  the  same  time  it  is 
to  be  remembered  that  no  very  large  bars 
have  yet  been  treated  electrically.  This 
process  has  so  far  been  applied  mainly  to 
the  production  of  comparatively  small 
cross-sections  of  metal,  although,  of  course, 
it  is  only  a  question  of  the  amount  of 
electric  power  to  permit  the  process  to  be 
carried  on  in  larger  sizes. 

The  power  required  to  heat  an  iron  or 
steel  bar  one  square  inch  in  cross -section 
and  20  inches  long  is  about  27  KW.  and 
requires  about  2^  minutes,  representing  a 
total  work  done  of  about  4,000,000  joules 
or  1|  KYVVhrg.  =  200,000  joules-per- 


262  ELECTRIC  HEATING. 

cubic-inch.  A  larger  bar  3  feet  long  and  3 
inches  in  diameter,  would  require  about 
75  KW.  over  ten  minutes,  or  45  megajoules 
-14  KW.  hours,  or  nearly  180,000  joules- 
per- cubic-inch. 

Two  distinctly  different  methods  are  in 
use  for  obtaining  the  electrical  heating  of 
the  material  to  be  shaped  or  forged;  name- 
ly, heating  it  by  passing  a  sufficiently 
powerful  current  through  it  while  in  the 
air,  and  passing  an  electric  current  from 
it  into  a  mass  of  surrounding  conducting 
liquid.  The  former  process,  as  in  electric 
welding,  requires  the  use  of  a  powerful 
current  strength  at  a  low  pressure  and  is 
best  obtained  by  means  of  an  alternating- 
current  transformer.  The  latter  process, 
on  the  contrary ,  requires  comparatively 
small  current  strength,  but  a  compara- 
tively high  electrical  pressure. 


MISCELLANEOUS  APPLICATIONS.  263 


FIG  83.— ELECTRIC  FORGE  AND  ELECTRIC  COOKING  RANGE. 


264  ELECTRIC  HEATING. 

Fig.  83  represents  the  apparatus  em- 
ployed when  the  former  method  of  heat- 
ing is  adopted.  T  T,  is  a  large  alternat- 
ing-current transformer  for  reducing  a 
current  of  comparatively  high  pressure  to 
one  of  very  low  pressure,  but  of  corre- 
spondingly increased  strength.  In  the 
particular  case  represented  the  primary 
coil  of  the  transformer  receives  about  40 
KW.  at  full  load  at  a  pressure  of  1500  volts 
and  consequently  a  current  strength  of 
about  24  amperes.  The  secondary  coil 
delivers  nearly  40  KW.  at  full  load  at  a 
pressure  of  about  4  volts  and,  consequent- 
ly, with  a  current  strength  of  about  10,000 
amperes.  The  secondary  terminals  of 
the  transformer  are  connected  with  the 
copper  massive  conductors  1  and  2 ;  3  and 
4;  5  and  6;  and  7  and  8;  any  pair  being  se- 
lected according  to  the  character  of  the 
work  to  be  heated,  These  conductors 


MISCELLANEOUS  APPLICATIONS.          265 

terminate  beneath  in  clamps  or  holders 
suitable  for  different  sizes  of  work.  Bars 
to  be  heated  are  shown  at  B,  bridging 
across  the  distance  between  the  two  elec- 
trodes or  clamps.  The  attention  of  the 
reader  is  called  to  the  electrical  cooking 
range  shown  at  the  right,  not  because  it 
has  any  connection  with  the  forging  proc- 
ess, but  from  the  fact  that  it  differs 
from  the  electric  cooking  ranges  de- 
scribed in  the  earlier  chapter  of  this 
book,  sin6e  its  heating  coils  are  properly 
proportioned  to  produce  the  required  tem- 
perature within  it  from  a  large  current 
strength  and  a  low  pressure  of,  say  four 
volts,  instead  of  from  a  high  pressure  of 
perhaps  100  volts,  and  a  correspondingly 
reduced  current. 

A  number  of  samples  of  work  done  by 
the  hammer  on  metal  heated  electrically 


266 


ELECTRIC  HEATING. 


FIG.  84.  —SAMPLES  OF  FORGINGS  ELECTRICALLY  HEATED. 


MISCELLANEOUS  APPLICATIONS.  267 

by    this   process  is    shown  in    Fig.   84. 

The  second  method  for  heating  consists 
in  plunging  the  metal  to  be  heated  be- 
neath the  surface  of  the  conducting  liquid, 
when  held  in  a  metal  clamp  connected  with 
the  negative  pole  of  a  continuous -current 
source  of  E.  M.  F.  The  metal  to  be  heated 
is  made  the  negative  pole,  and  the  ves- 
sel containing  the  liquid  is  provided  with 
a  metal  lining  of  lead  connected  with  the 
positive  pole.  Under  these  circum- 
stances the  current  passes  from  the  liquid 
to  the  metal  to  be  heated.  The  current 
strength  employed  is  sufficient  to  produce 
free  electrolysis  of  the  liquid  with  the 
production  of  free  hydrogen  gas  at  the  sur- 
face of  the  metal  to  be  heated,  the  high 
resistance  of  which  causes  so  intense  a 
heat  at  this  surface  as  to  practically  set  up 
an  electric  arc  over  its  surface.  The  heat 
so  produced  rapidly  penetrates  the  mass 


268  ELECTBIC  HEATING. 

of  the  metal  and  raises  its  temperature. 
It  is  to  be  observed  that  this  method 
can  only  be  employed  with  a  continuous 
current.  The  heating  process  is  con- 
ducted without  any  oxidation  of  the  metal 
to  be  heated,  its  surface  being  thoroughly 
protected  by  the  enveloping  mass  of  hy- 
drogen. The  metal  surface  of  the  vessel 
containing  the  liquid  becomes  oxidized  by 
electrolysis  during  the  operation  of  the 
process,  and  has  to  be  renewed  from  time 
to  time .  T  he  main  resistance  in  this  liquid 
tank  exists  at  the  surface  of  the  metal,  in 
the  film  or  layer  of  hydrogen,  and,  conse- 
quently, it  is  at  this  surface  that  the  heat 
is  almost  entirely  liberated.  Consequent- 
ly, the  amount  of  current  employed  is 
automatically  regulated  by  the  surface 
area  of  the  immersed  metal,  the  larger  the 
surface  the  greater  the  current  strength 
which  will  flow.  The  pressure  employed 


MISCELLANEOUS  APPLICATIONS. 


269 


for  such  a  liquid  heater  may  be  from  100 
to  500  volts,  and  the  current  strength  from 
45  amperes  upward. 

In  order  to  render  the  liquid  conduct- 
ing, a  suitable  conducting  salt  such  as  sal 
soda  is  dissolved  in  the  water  to  a  specific 


- 


=£$£=======:  SB  * 


FIG.  85. — END  VIEW  OF  HEATING  TANK. 

gravity  of  1.2  at  84°  F.,  and  to  every  ten 
gallons  of  the  solution  five  pounds  of 
borax  are  added. 

Fig.  85  represents  an  end  view  in  cross - 
section  of  the  tank  employed.     The  pin- 


270 


ELECTBIC  HEATING-. 


cers  P,  are  connected  with  the  positive  pole 
of  the  source  and  hold  the  metal  article 
M,  so  that  this  is  partially  submerged. 
The  negative  pole  N,  is  connected  with 


FIG.  86.  —PLAN  OF  HEATING  TANK. 

the  sheet  lead  lining  of  the  tank.  Fig.  86 
represents  the  same  apparatus  in  plan 
view. 

THE   END. 


INDEX. 


A. 

Abnormal  Temperature  Elevation  of  Circuits,  How 

Avoided,  87,  89. 
Acetyline  Gas,  Illuminating  Power  of,  244. 

— ,  Production  of,  from  Calcium  Carbide,  243,  244. 
Activity,  Definition  of,  26. 

— ,  Muscular,  Obtained  from  the  Sun,  15. 

—  of  Circuit,  41. 

—  of  Electric  Circuit,  35. 
-  of  Laborer,  27. 

— ,  Unit  of,  26. 
Aerial  Dare  Wires,  Effect  of  Character  of  Surface  on 

Temperature  Elevation  of,  6G. 
— ,  Effect  of  Extent  and  Surface  on  Temperature 

Elevation  of,  6fi. 
Affinity,  Chemical,  9. 
Air  Heater,  Portable  Elect- ic,  133,  134. 

,  Resistance  Offered  by  to  Escape  of  Heat  from 

Conductors,  59,  60. 


272  ELECTRIC  HEATING. 

Alloys,  Effect  of  Temperature  on  Resistivity  of,  56, 57. 

— ,  Lead-Tin,  for  Fuse  Wires,  91. 
Alternating  Current,  Definition  of,  201. 
Alternating  Currents,  Advantages  Possessed  by,  for 

Electric  Heating,  189,  190. 
Alternator  for  Indirect  Welding,  199,  200. 

— ,  Separately-Excited,  200. 
Aluminum,    Alloys,    Furnace    for    Production    of, 

244-247. 

— ,  Metallic,  Electric  Production  of,  247-249. 
Ampere  or  Coulomb-per-Secofid,  35. 
Annealing,  Electric,    of  Harveyized  Armor  Plates, 

255-257. 

— ,  Influence  of,  on  Resistivity,  54. 
Armor  Plates,  Harveyized,  Electric   Annealing   of, 

255,  256. 

Atlantic  Liner,  Activity  of  Driving  Engines  of,  27. 
Atmospheric  Heater,  137. 
Automatic  Welder,  206-208. 

B. 

B.  T.  U.,  29. 

Back  Electric  Pressure,  41. 

Banquet,  Franklin's  Electrically  Cooked,  178,  180. 
Bare  Aerial  Wires,  Temperature  Elevation  of,  45,  46. 
—  Conductors,  Electrical  Heating  of,  37-68. 


INDEX.  273 

Block,  Ceiling,  105. 

— ,  Porcelain,  87-98. 

— ,  Safety  Fuse,  86. 

,  Cut-Out,  106,  107. 

Bond  for  Street  Railways,  219. 
Box,  Cut-Out,  107. 
Branch  Fuse,  113,  114. 
British  Heat  Unit,  29. 

-  Thermal  Unit,  29. 

-  Thermal  Unit,  Value  of,  29. 

Buried  Conductor,  Permissible  Temperature  Eleva- 
tion of,  85. 

c. 

C.  E.  M.  F.,  42. 

— ,  Development  of,  by  Motor,  45. 

—  in  Circuit,  Distribution  of,  42,  43. 
Cable  Welder,  213. 
Calcium  Carbide,  Furnace  for  Manufacture  of,  242, 

243. 

Calking,  Electric,  231,  232. 
Calorie,  Lesser,  29. 

Capacity,  Carrying,  of  Conductor,  75. 
Car  for  Direct  Welding,  222. 

-  Heater,  Electric,  125, 12G. 

-  Heaier  Regulating  Switch,  127, 129,  21S. 
Heating,  Cost  of,  142-145. 


274  ELECTKIC    HEATING. 

Carbon, Effect  of  Temperature  on  Resistivity  of,  56,57. 
Carborundum,  237. 

Furnace,  238-241. 

Carriage  Axle  Welder,  212. 

-Tire  Welder,  21  >,  211. 
Carrying  Capacity  of  Fuse  Wires,  92. 
Castings,  Sharpness  of,  When  Produced  from  Elec- 
trically Fused  Metals,  251. 
Ceiling  Fixture,  Fuse-Block,  104,  105. 
Chafing  Dish,  Electric,  164. 
Chemical  Affinity,  9. 
Circuit,  Activity  of,  40. 

— ,  C.  E.  M.  F.  and  Activity  of,  46,  47. 

— ,  Distribution  of  C.  E.  M.  F.  in,  42,  43. 
,  Wires,  Bare,  64. 

— ,  Wires,  Covered,  64. 
Circular  Mils,  Definition  of,  52. 
Coal,  Energy  in  Pound  of,  10, 11. 
— ,  Origin  of  Energy  in,  12. 
Coal-Beds,  {Store-houses  of  Solar  Energy,  13,  14. 
Coffee  Heater,  Electric,  157. 
Coffee-Pot,  Electric,  158. 
Compound-Wound  Machine,  200. 
Conduction,  Loss  of  Heat  by,  63. 
Conductor,  Carrying  Capacity  of,  75. 
,  Temperature  Elevation  of,  62. 


INDEX. 


Conductors,  Pure  Metallic  EffeclN&Xepiperature  on 

Kes' stivity  of,  56,  57. 
— ,  Transmission,  Nece  sity  for  Maintain 
Temperature  of,  69. 

Conduits  for  Insulated  Wires,  77. 

Connections  for  Indirect  Welding,  198. 

CoLvection,  Approximate  Amount  of  Heat  Lost  by 
Conductor  per  Foot  of  Length  per  Sec- 
ond, 67. 

— ,  Loss  of  H  eat  by,  63. 

— ,  Lnss  of  Heat,  Practical  Independence  of  Ex- 
tent and  Character  of  Surface  on  Temper- 
ature Elevation  of,  66,  67. 

Convectional  Losses  in  Conductors,  Effect  of  Motion 
of  Air  on,  68. 

Cooking,  Electric,  151-180. 

Copper- Tipped  Fuse  Wiret>,  95. 

Cost  of  Car  Keating,  142-145. 

Coulomb,  or  Unit  of  Electric  Quantity,  32. 

Coulomb- Volts  or  Unit  of  Electric  Work,  33. 

Counter  E.  M.  F.,  41. 

-  E.  M.  F.,  how  Produced,  44-45. 

Counter- Hydraulic  Pressure,  40,  41. 

Covered  Conductors,  Electrical  Heating  of,  69-86. 

Curling-Tongs  Heater,  Electric,  177, 178. 

Current,  Electric,  Work  done  by,  33. 


276  ELECTKIC  HEATING. 

Current  Strength,  Effect  of,  on  Temperature  Eleva- 
tion of  Wire  80. 

—  Strength,  Effective. 

—  Strength,  Thermal,  62. 
Cut-Out  Box,  107. 

Cylindrical  Electric  Heater,  120-122. 

D. 

Diameters  of  Fuse  Wires,  92. 

Diamonds,  Electric  Furnace  for  the  Production  of 

Artificial,  253.  254. 
Difference  of  Electrical  Pressure,  Electrical  Flow 

Produced  by,  32. 

—  of  Thermal  Pressure,  72. 

—  of  Water  Level,  Liquid  Flow  Produced  by,  31. 
Direct  Welder,  191-193. 

-  Welder,  Electric,  223. 

-  Welding  Apparatus,  194-196. 

-  Welding  Car,  222 . 
Dissipation  of  Heat,  9. 

Doctrine  of  the  Conservation  of  Energy,  20. 
Drop,  Definition  of,  43. 

E. 

E.  M.  F.,  35. 

— ,  Counter,  41. 
— ,  Impressed,  41. 


INDEX.  277 

Earth-Buried  Conductors,  Lo&sof  Heat  by,  81. 

Economy  of  Electric  Smelting,  252. 

Effective  Thermal  Resistance  of  Earth- Buried  Con- 

ductois,  81. 
Efficiency  of  Electric  Kettle,  152. 

—  of  Steam  Engine,  11. 
Electric  Boiling  of  Water,  Cost  of,  161. 
Car  Heater,  125,  126. 

Circuit,  Activity  of,  35. 

-  Cooking,  151-180. 

—  Cooking,  Advantages  of,  172,  173. 

-  Heaters,  117-150. 

—  Heater,  Advantages   Possessed   by,    for  Ca*1 

Heating,  124. 

-  Heater,  Advantages  of,  J19. 

-  Radiator,  123. 

-  Resistance,  38. 

-  Source,  Definition  of,  24. 

Electricity  and  Heat,  Relations  between,  19,  20. 

—  Circumstances  Regulating  Flow  of,  37. 
Electrolysis,  Definition  of,  236. 
Electrolytic  Heating,  267-269. 
Electromotive  Force,  Definition  of,  32. 
Elements  of  Work,  22. 

Energy,  Conservation  of,  20. 
in  Pound  of  Coal,  10,  11. 


278  ELECTRIC  HEATING. 

Energy,  of  Coal,  Origin  of,  12. 

—  Storage  of,  in  Water  Reservoir,  30. 


F. 


Falling  Water,  Storage  of  Solar  Energy  in,  16. 

Fan,  Electric,  1 54-150. 

Feeders,  Ground,  for  Electric  Railways,  220. 

Flexible  Electric  Hea  er,  146,  147. 

Flow  of  Electricity,  Circumstances  Regulating,  37. 

—  of  Water,  Circumstances  Regulating,  37. 
Foot-Pound-per-Second,  Definiti  m  of,  26. 
Foor-Pounds,  23. 
Force,  Definition  of,  21. 

— ,  Electromotive,  Definition  of,  32. 
Forging,  Electric,  263,  264. 

— ,  Electric,  of  Metals,  259,  260. 

— ,  Electi  ic,  Samples  of,  266. 
Franklin's  ElectiicallyC  oked  Banquet,  178-180.' 
Full-Load  Current,  Temperature  Elevation  uuder,80. 
Furnace,  Electric,  233-254. 

— ,  Electric,  Definition  of,  233. 

— ,  Electric,  for  Manufacture  of  Calcium  Carbide, 
242,  243. 

— -,  Electric,  for  the   Manufacture  of  Carborun- 
dum, 238-241. 


INDEX.  279 


Fuse-Box,  Ceiling  Fixture,  104, 105. 

-  Boxes,  Mica-Covered,  100,  101. 

-  Boxes,  Porcelain-Covered,  102, 103. 
— ,  Branch,  113, 114. 

-  Links,  94. 

— ,  Main-Circuit,  113,  114. 
—  Screw  Block,  107. 

-  Wire,  Definition  of,  89. 

—  Wire  Strips,  93. 

-  Wires,  87-115. 

—  Wires,  Copper-Tipped,  95. 

~  Wires,  Carrying  ( 'apacity  of,  92. 

-  \Vires,  Composition  of,  91. 
Wires,  Diameters  of,  9'2. 


Fuses,  Safety,  90. 

G. 

Glue-Pot,  Electrically  Heated.  175. 
Ground-Feeders  for  Electric  Railways,  220. 

H. 

Harveyized  Armor  Plates,    Electric  Annealing  of 

255-257. 
Heat  and  Electricity,  Kelations  between,  19,  20. 


280  ELECTRIC  HEATING. 

Heat   and  Mechanical  Work,  Relations    between, 
17,  18. 

—  Conduction,  63. 

— ,  Dissipation  of,  9. 

— ,  Loss  of,  by  Conduction,  63. 

— ,  Loss  of,  by  Convection,  63. 

— ,  Loss  of,  by  Eadiation,  64. 

— ,  Nature  of,  8. 

— ,  or  Molecular  Oscillations,  9. 
-  Unit,  British,  °/J. 

— ,  Unit  of,  28,  29. 
Heater,  Cylindrical,  Electric,  120-J22. 

— ,  Electrical,  Advantages  of,  119. 

— ,  Electric  Tank,  141,  142. 

— ,  Electric  Wall,  138. 

— ,  Flexible  Electric,  146,  147. 

— ,  Portable  Electric,  140,  141. 
Heaters,  Electric,  117-150. 

— ,  Electric,  Essential  Construction  of,  119. 

— ,  E  ectric,  Kequisites  for,  119. 
Heating,  Electric-  Coil  Conductor  for,  122. 

— ,  Electric,  Tank  for,  26'),  270. 

— ,    Electric,    Miscellaneous    Applications      of, 
255-270. 

— ,  Electrical,  of  Bare  Conductors,  37-68. 

— ,  Electrical,  of  Covered  Conductors,  69-86. 


INDEX.  281 

Heating  of  Conductor,  Effect  of  Insulating  Covering 
on,  69,  70. 

,  Electrolytic,  267-269. 

Hemp  Covered  Wires,  Permissible  Temperature  Ele- 
vation of,  85. 

Horse-Power  and  Kilowatt,  Relative  Values  of,  36. 

,  Definition  of,  26  27. 

Hydraulic  Resistance,  38. 

I. 

Impressed  E.  M.  F.,  41. 

Indirect  Welder,  197,  198. 

Welding,  192. 

Welding,  Connections  for,  198. 

Insulated  Wires,  Conduits  for,  77. 

Wires  in  Conduits,  Temperature  Elevation  of, 

77. 

Wires,  Mouldings  for,  76,  77. 

Insulating  Covering,  Effect  of,  on  Electrical  Heating 
of  Conductor,  69. 

Covering,  Effect  of  Thickness  of,  on  Tempera- 
ture Elevation,  72. 

Covering,  Thermal  Resistance  of,  72. 

International  Unit  of  Activity,  26,  27. 
J. 

Joints,  Welded,  Tensile  Strength  of,  187. 


282  ELECTRIC  HEATING. 

Joule,  33. 

— ,  Definition  of,  24,  25. 
—  per-Second,  26,  27. 
— ,  Value  of,  in  Foot- Pounds,  25. 

K. 

Kettle,  Electric,  158. 

— ,  Electric,  Efficiency  of,  1G2. 
Kilowatt,  36. 
Kitchen,  Electric,  169-171. 

L. 

Laborer,  Activity  of,  27. 
Law,  Ohm's,  39. 

Lead  Sheathing  of  Wires,  Influence  of,  on  Tempera- 
ture Elevation  of,  74. 
Lead-Tin  Alloys  for  Fuse  Wires,  91. 
Lesser  Calori",  23. 
Level,  Electric,  Difference  of,  32. 
Links,  Fuse,  94. 
Loss  of  He  it  by  Conduction,  63. 

of  Heat  by  Convection,  63. 

of  Heat  by  Badi  ition,  63,  64. 

M. 

Mechanical  Work  and  Quantity  of  Heat,  Relations 
between,  17,  18. 


INDEX.  283 

Megajoule,  Definition  of,  206. 

Metallic  Ores,  Electric  Production  of,  250,  251. 

Metals,  Electric  Fogging  of,  258-260. 

— ,  Electrical  Working  of,  259-270. 
Mica-Covered  Fuse  Boxes,  100,  101. 
Microhm,  Definition  of,  48. 
Mil,  Definition  of,  51,  52. 
Mils,  Circular.  Definition  of,  52. 
Molecular  Oscillations  or  Heat,  9. 
Motor,  Electric  Development  of  Counter  E.  M.  F. 
by,  45. 

— ,  Dynamo,  221. 
Mouldings  for  Insulated  Wire,  76,  77. 

— ,  Wooden,  Rule  for  Size  of  Wire  in,  77,  78. 

N. 

Nature  of  Heat,  8. 

Negative  Eesistivity,  Temperature  Coefficient  of,  56. 

0. 

Oce  in  Cables,  Temperature  Elevation  of,  86, 
Ohm's  Law,  33. 

P. 

Pan-Cake  Griddles,  Electric,  166. 
Physical  State,  Influence  of,  on  Resistivity,  54. 
Pipe-Bending  Apparatus,  Electric,  218. 
Plug-Switch  for  Electric  Heaters,  168,  169. 


284  ELECTRIC  HEATING:. 

Porcelain-Covered  Fuse- Boxes,  102,  103. 

-  Fuse-Block,  97,  98. 
Portable  Electric  Heater,  133,  134. 

-  Electric  Heater,  140, 141. 

Positive  Resistivity,  Temperature  Coefficient  of,  56. 
Press  n  re,  Back  Electric,  41. 

— ,  Counter-Electric,  41. 
,  Counter- Hydraulic,  40,  41. 

— ,  Electric,  Difference  of,  32. 

— ,  Hydraulic,  40,  41. 

— ,  Unit  of  Electric,  33. 
Primary  Coils  of  Transformer,  201. 
Purity,  Influence  of,  on  Resistivity,  54. 

Q. 

Quantity,  Electrical,  Unit  of,  32. 

E. 

Radiation,  Loss  of  Heat  by,  63,  64. 
Radiator,  Electric,  122,  123. 
Rails,  Elec'rically  Welded,  22G. 
Rate  of  Doing  Work,  or  Activity,  26. 
Reduction,  Electric,  of  Metallic  Ores,  250,  251. 
Regulating  Switch  for  Car  Heater,  127-129. 
Reservoir  of  Water,  Activity  in,  34,  35. 


285 


Resistance,  Electric,  38. 

—  ,  Hydraulic,  38. 

-  ,  Thermal,  of  Insulating  Covering,  71. 
Resistivity,  Definition  of,  48. 

—  ,  Effect  of,  on  Pure  Metallic  Conductors,  56.  57. 

-  ,  Effect  of  Temperature  on,  5G,  57. 

—  ,  Influence  of  Annealing  or.,  54. 

—  ,  Influence  of  Physical  Sta'e  on,  54. 
---  ,  Influence  of  Purity  on,  54. 

—  of  Alloys,  Effect  of  Temperature  on,  56,  57. 

—  of  Carbon,  Effect  of  Temperature  on,  56,  57  . 
Rotary  Transformer,  221. 

Rubber  Covered  Wires,   Permissible  Temperature 

Elevation  in,  85. 
Rule  for  Size  of  Wire  in  Wooden  Mouldings,  77,  78. 

s. 

Sad  Iron,  Electric,  176. 
Safety  Fuse-Block,  96. 

-  Fuses,  90. 

—  Stiips,  93. 

--  Transformer  Fuse-  Box,  109,  110. 
Screw  Block,  107. 

Sealing-  Wax  Heater,  Electric,  177. 
Secondary  Coils  of  Transformer,  201. 
Separately  -Excited  Alternator,  200. 


286  ELECTRIC  HEATING. 

Sharpness  of  Castings  When  Producdby  Electrical- 
ly-Fused Metals,  251. 
Shrapnel  Shells,  Welder  for,  217,  218. 
Size  of  Wire  in  Wooden  Moulding,  Rule  for,  77,  78. 
Skillet,  Electric,  160. 
Smelting,  Electric,  Economy  of,  256. 
Socket  Attachment,  107. 
Solar  Energy,  St  >rage  of,  in  Coal  Beds,  13, 14. 

—  Energy,  Stjrage  of,  in  Falling  Water,  16. 

Energy,  f-  torage  of,  in  Wind,  16. 

Soldering,  Electric,  230,  257-259. 
Source,  E  ecttic,  Definition  of,  32. 
Specimens  of  Electric  Welding,  215. 
Steam  Cooker,  Electric,  167. 
Stearn  Engine,  Efficiency  of,  11. 
Step-Down  Transformer,  190. 
Stew  Pan,  Electric,  165. 
Street  Railway,  Bonds  for,  219. 
Strips,  Fuse  Wire,  93. 

— ,  Safety,  93. 
Subdivided  Conductors,  Temperature  Elevation    of, 

75,  76. 

Subway,  Temperature  Elevation  of  Wires  in,  82. 
Sun,  Prime  Source  of  Muscular  Activity,  15. 
Switch,  Car  Heater  Regulating,  127. 
for  Electric  Fan,  155. 


INDEX. 


287 


T. 

Table  of  Resistivities,  48,  49. 
Tank  for  Electric  Heating,  269,  270. 

-Heater,  Electric,  141,  142. 

Temperature,  Effect  of,  on  Pure  Metallic  Conductors, 
56,  57. 

— ,  Effect  of,  on  Resistivity,  56,  57. 

— ,  Effect  of,  on  Resistivity  of  Alloys,  56,  57. 

-  Elevation  of  Circuits,  Abnormal,  How  Avoid- 

ed, 87,  89. 

—  Elevation  of  Conductor,  62. 

-  Elevation  of  Conductor,  Effect  of  Thickness 

of  Insulating  Covering  on,  72. 

-  Elevation  of  Conductors  in  Conduits,  77. 

—  Elevation  of  Ocean  Cables,  86. 

-  Elevation  of  Subdivided  Conductors,  75,  76. 

—  Elevation  of  Wire,  Effective  Cuireut  Strength 

of,  80. 

—  Elevation  of  Wire,  Maximum  Time  Required 

for.  83,  84. 

-  Elevation  of  Wire,  Safe,  79. 
Elevation  of  Wires  in  Subway,  82. 

-  Elevation     Permissible     in     Hemp-Covered 

Wires,  85. 

Elevation   Permissible    in     Rubber-Covered 
Wires,  85. 


ELECTRIC  HEATING. 

Temperature,  Elevation,  Permissible,  in  Buried  Con- 
ductors, 8i,  85. 

Tensile  Strength  of  Electrically  Welded  Joints,  187. 
Therm,  Defination  of   29. 
Thermal  Current  Strength,  62. 

-  Resistance,  Effective,  of  Earth  Buried  Con- 

ductors, 81. 

-  Resistance  of  Insulating  Covering,  71. 
Unit,  British,  '29. 

Tin- Lead  Alloys  for  Fuse  Wires.  91. 
Transformer,  Primary  Coils  of,  201. 

— ,  Rotary,  22 1. 

— ,  Safety  Fuse  Box,  109,  110. 
— ,  Secondary  Coils  of,  201. 

— ,  Step-Down,  190. 
,  Welding,  201-206. 

u. 

Unit,  British  Heat,  29. 

-  Heat,  29. 

-  of.  Activity,  26. 

—  of  Activity,  International,  26,  27. 
Units  of  Work,  23. 
Universal  Welder,  211. 

V. 

Vegetable  Food,  Store-houses  of  Solar  Energy,    14, 
15. 


INDEX.  289 

Volt,  or  Unit  of  Electric  Pressure,  32,  33. 

—  Ampere  or  Watt,  36. 

—  Coulornb-per-Second,  36. 

w. 

Wall  Heater,  Electric,  138. 

\Vater,  Circumstances  Regulating  Flow  of,  37. 

— ,  Conditions  Requisite  for  Causing  Flow  of,  31. 

—  Gram  me- Degree-Centigrade,  29. 

-  Heater,  Electric,  Low  Economy  of,  162,  163. 

—  in  Reservoir,  Capacity  of,  for  doing  Work,  30. 

—  Reservoir,  Storage  of  Energy  in,  30. 

— ,  Resistance  Offered  by,  to  Escape  of    Heat 

from  Conductors,  58,  59. 
Watt,  Definition  of,  26,  27, 

— ,  or  Volt-Ampere,  36. 
Welder,  Automatic,  206-208. 

— ,  Direct,  191-193. 

-for  Cables,  213. 
for  Carriage  Axle,  212. 

-  for  Carriage  Tires,  210,  211. 

-  for  Shrapnel  Shells,  217,  218, 

-  for  Wheel  Spokes,  214. 

,  Indirect,  197,  198. 

,  Universal,  211. 


290  ELECTEIC  HEATING. 

Welding,  Advantages  Possessed  by  Alternating  Cur- 
rents in,  189. 
-  Apparatus,  Direct,  194-196. 

,  Conditions  Requisite  foi  Obtaining  Efficient 

Joints  by,  183,  184. 

,  Definition  of,  182,  183. 

— ,  Electric,  181-232. 

,  Electric,  Advantages  Possessed  by,  185,  186 

t  Electric,  Use  of  C  mtinuous  or  Alternating 

Cunentsin,  187,  188. 

Transformer,  201-206. 

Wheel  Spokes,  Welder  for,  214. 

Wind,  Storage  of  Solar  Energy  in,  16. 

Wires,  Bare  Circuit,  64. 

,  Covered  Circuit,  64. 

,  Fuse,  87-115 

f  Safe  Temperature  Elevation  of,  79. 

Work,  Definition  of,  22. 

done  by  Electric  Current,  33. 

,  Elements  of,  22. 

,  Units  of,  23. 

,  Unit  of,  Electric,  33. 

Working  of  Electrical  Metals,  259-270, 

z. 

Zoroaster,  7. 


Elementary 
Electro -Technical  Series. 

BY 

EDWIN  J,  HOUSTON,  Ph.D,  and  A,  E.  KENNELLY,  D.Sc. 


Alternating  Electric  Currents,  Electric  Incandescent  Light- 
Electric  Heating,  ing, 

Electromagnetism,  Electric  Motors, 

Electricity  in   Electro-Thera-  Electric  Street  Railways, 

peutics,  Electric  Telephony, 

Electric  Arc  Lighting,  Electric  Telegraphy. 


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THIRD  EDITION.      GREA  TL  Y  ENLAR  GED. 
A  DICTIONARY  OF 

Electrical  Words,  Terms, 
and  Phrases. 

By  EDWIN  J.  HOUSTON,  Ph.D.  (Princeton). 

AUTHOR  OF 

"Advanced  Primers  of  Electricity";    '•'Electricity   One 
Hundred  Years  Ago  and  To-day,*'  etc.,  etc. 

Cloth,  667   large   octavo   pages,    582    illustrations, 
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stated  that  it  contains  definitions  of  about  6000  distinct  words, 
terms,  or  phrases.  The  dictionary  is  not  a  mere  word-book  ;  the 
words,  terms,  and  phrases  are  invariably  followed  by  a  short,  cen- 
cise  definition,  giving  the  sense  in  which  they  are  correctly  employed, 
and  a  general  statement  of  the  principles  of  electrical  science  on 
which  the  definition  is  founded.  Each  of  the  great  classes  or  di- 
visions of  electrical  investigation  or  utilization  comes  under  careful 
and  exhaustive  treatment ;  and  while  close  attention  is  given  to  the 
more  settled  and  hackneyed  phraseology  of  the  older  branches  of 
work,  the  newer  words  and  the  novel  departments  they  belong  to 
are  not  less  thoroughly  handled.  Every  source  of  information  has 
been  referred  to,  and  while  libraries  have  been  ransacked,  the  note- 
book of  the  laboratory  and  the  catalogue  of  the  wareroom  have  not 
been  forgotten  or  neglected.  So  far  has  the  work  been  carried  in 
respect  to  the  policy  of  inclusion  that  the  book  has  been  brought 
down  to  date  by  means  of  an  appendix,  in  which  are  placed  the 
very  newest  words,  as  well  as  many  whose  rareness  of  use  had  con- 
signed them  to  obscurity  and  oblivion. 

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Electricity   and   Magnetism. 

A  Series  of  Advanced  Primers. 

By  EDWIN  J.  HOUSTON,  PH.D.  (Princeton). 

AUTHOR   OF 

"A   Dictionary  of  Electrical  Words,    Terms  and  Phrases," 
etc.)  etc.,  etc. 

Cloth.        306  pages.         116  illustrations.        Price,  $1.00. 


During  the  Philadelphia  Electrical  Exhibition  of  1884,  Prof 
Houston  issued  a  set  of  elementary  electrical  primers  for  the  benefit 
of  the  visitors  to  the  exhibition,  which  attained  a  wide  popularity. 
During  the  last  ten  year?,  however,  the  advances  in  the  applications 
of  electricity  have  been  so  great  and  so  widespread  that  the  public 
would  no  longer  be  satisfied  with  instruction  in  regard  to  only  the 
most  obvious  and  simple  points,  and  accordingly  the  author  has 
prepared  a  set  of  new  primers  of  a  more  advanced  character  as  re- 
gards matter  and  extent.  The  treatment,  nevertheless,  remains 
such  that  they  can  be  easily  understood  by  any  one  without  a  pre- 
vious knowledge  of  electricity.  Electricians  will  find  these  primers 
of  marked  interest  from  their  lucid  explanations  of  principles,  and 
the  general  public  will  find  in  them  an  easily  read  and  agreeable 
introduction  to  a  fascinating  subject.  The  first  volume,  as  will  be 
seen  from  the  contents,  deals  with  the  theory  and  general  aspects 
of  the  subject.  As  no  mathematics  is  used  and  the  explanations 
are  couched  in  the  simplest  terms,  this  volume  is  an  ideal  first  book 
from  which  to  obtain  the  preliminary  ideas  necessary  for  the 
proper  understanding  of  more  advanced  works. 

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The  Measurement  of  Electrical  Cur- 
rents and  Other  Advanced 
Primers  of  Electricity. 

By  EDWIN  J.  HOUSTON,  PH.D.  (Princeton). 

AUTHOR  OF 

"  A    Dictionary    of   Electrical    Words,     Terms t    and 
Phrases"  etc,,  etc.,  etc. 

Cloth,     429  pages,  169  illustrations.      Price,  $1,00, 


This  volume  is  the  second  of  Prof.  Houston's  admirable  series 
of  Advanced  Primers  of  Electricity ',  and  is  devoted  to  the  meas- 
urement and  practical  applications  of  the  electric  current.  The 
different  sources  of  electricity  are  taken  up  in  turn,  the  apparatus 
described  with  reference  to  commercial  forms,  and  the  different 
systems  of  distribution  explained.  The  sections  on  alternating 
currents  will  be  found  a  useful  introduction  to  a  branch  which  is 
daily  assuming  larger  proportions,  and  which  is  here  treated  with- 
out the  use  of  mathematics.  An  excellent  feature  of  this  series  of 
primers  is  the  care  of  statement  and  logical  treatment  of  the  sub- 
jects. In  this  respect  there  is  a  marked  contrast  to  most  popular 
treatises,  in  which  only  the  most  simple  and  merely  curious  points 
are  given,  to  the  exclusion  or  subordination  of  more  imporiant 
ones.  The  abstracts  from  standard  electrical  authors  at  the  end  of 
each  primer  have  in  general  reference  and  furnish  an  extension  to 
some  important  point  in  the  primer,  and  at  the  same  time  give  the 
reader  an  introduction  to  electrical  literature.  The  abstracts  have 
been  chosen  with  care  from  authoritative  professional  sources  or 
from  treatises  of  educational  value  in  the  various  branches. 

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Electrical  Transmission 
of  Intelligence 

AND  OTHER  ADVANCED  PRIMERS  OF  ELECTRICITY, 
By  EDWIN  J.  HOUSTON,  PH.D.  (Princeton), 

AUTHOR  OF 

"  A    Dictionary    of   Electrical    Words,     Terms,    and 
Phrases"  etc.,  etc.,  etc. 

Cloth.      33o  pages,  88  illustrations.      Price,  $1.00. 


The  third  and  concluding  volume  of  Prof.  Houston's  series  of 
Advanced  Primers  of  Electricity  is  devoted  to  the  telegraph,  tele- 
phone, and  miscellaneous  applications  of  the  electric  current.  In 
this  volume  the  difficult  subjects  of  multiple  and  cable  telegraphy 
and  electrolysis,  as  well  as  the  telephone,  storage  battery,  etc.,  are 
treated  in  a  manner  that  enables  the  beginner  to  easily  grasp. the 
principles,  and  yet  with  no  sacrifice  in  completeness  of  presenta- 
tion. The  electric  apparatus  for  use  in  houses,  such  as  electric 
bells,  annunciators,  thermostats,  electric  locks,  gas-lighting  systems, 
etc.,  are  explained  and  illustrated.  The  primer  on  electro-thera- 
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as  well  as  explaining  the  action  of  various  currents  on  the  human 
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ELECTRICITY 

ONE  HUNDRED  YEARS  AGO  AND  TO-DAY. 

By  EDWIN  J.  HOUSTON,  PH.D.  (Princeton), 

AUTHOR   OF 

"A    Dictionary    of    Electrical    Words,    Terms,    and 
Phrases,"  etc.,  etc.,  etc. 

Cloth,       179  pages,  illustrated,        Price,  $1,00, 


In  tracing  the  history  of  electrical  science  from  practically  its 
birth  to  the  present  day,  the  author  has,  wherever  possible,  con- 
sulted original  sources  of  information.  As  a  result  of  these 
researches,  several  revisions  as  to  the  date  of  discovery  of  some  im- 
portant principles  in  electrical  science  are  made  necessary.  While 
the  compass  of  the  book  does  not  permit  of  any  other  than  a  general 
treatment  of  the  subject,  yet  numerous  references  are  given  in  foot- 
notes, which  also  in  many  cases  quote  the  words  in  which  a  dis- 
covery was  first  announced  to  the  world,  or  give  more  specific  in- 
formation in  regard  to  the  subjects  mentioned  in  the  main  portion 
of  the  book.  This  feature  is  one  of  interest  and  value,  for  often  a 
clearer  idea  may  be  obtained  from  the  words  of  a  discoverer  of  a 
phenomenon  or  principle  than  is  possible  through  other  sources. 
The  work  is  not  a  mere  catalogue  of  subjects  and  dates,  nor  is  it 
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to  great  names  in  electrical  science.  Much  information  as  to  elec- 
trical phenomena  may  also  be  obtained  from  the  book,  as  the  author 
is  not  satisfied  to  merely  give  the  history  of  a  discovery,  but  also 
adds  a  concise  and  clear  explanation  of  it. 

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